1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2005 John Baldwin <[email protected]>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 *
28 * $FreeBSD$
29 */
30
31 #ifndef __SYS_REFCOUNT_H__
32 #define __SYS_REFCOUNT_H__
33
34 #include <sys/limits.h>
35 #include <machine/atomic.h>
36
37 #ifdef _KERNEL
38 #include <sys/systm.h>
39 #else
40 #include <stdbool.h>
41 #define KASSERT(exp, msg) /* */
42 #endif
43
44 static __inline void
refcount_init(volatile u_int * count,u_int value)45 refcount_init(volatile u_int *count, u_int value)
46 {
47
48 *count = value;
49 }
50
51 static __inline void
refcount_acquire(volatile u_int * count)52 refcount_acquire(volatile u_int *count)
53 {
54
55 KASSERT(*count < UINT_MAX, ("refcount %p overflowed", count));
56 atomic_add_int(count, 1);
57 }
58
59 static __inline __result_use_check bool
refcount_acquire_checked(volatile u_int * count)60 refcount_acquire_checked(volatile u_int *count)
61 {
62 u_int lcount;
63
64 for (lcount = *count;;) {
65 if (__predict_false(lcount + 1 < lcount))
66 return (false);
67 if (__predict_true(atomic_fcmpset_int(count, &lcount,
68 lcount + 1) == 1))
69 return (true);
70 }
71 }
72
73 static __inline bool
refcount_release(volatile u_int * count)74 refcount_release(volatile u_int *count)
75 {
76 u_int old;
77
78 atomic_thread_fence_rel();
79 old = atomic_fetchadd_int(count, -1);
80 KASSERT(old > 0, ("refcount %p is zero", count));
81 if (old > 1)
82 return (false);
83
84 /*
85 * Last reference. Signal the user to call the destructor.
86 *
87 * Ensure that the destructor sees all updates. The fence_rel
88 * at the start of the function synchronized with this fence.
89 */
90 atomic_thread_fence_acq();
91 return (true);
92 }
93
94 /*
95 * This functions returns non-zero if the refcount was
96 * incremented. Else zero is returned.
97 *
98 * A temporary hack until refcount_* APIs are sorted out.
99 */
100 static __inline __result_use_check bool
refcount_acquire_if_not_zero(volatile u_int * count)101 refcount_acquire_if_not_zero(volatile u_int *count)
102 {
103 u_int old;
104
105 old = *count;
106 for (;;) {
107 KASSERT(old < UINT_MAX, ("refcount %p overflowed", count));
108 if (old == 0)
109 return (false);
110 if (atomic_fcmpset_int(count, &old, old + 1))
111 return (true);
112 }
113 }
114
115 static __inline __result_use_check bool
refcount_release_if_not_last(volatile u_int * count)116 refcount_release_if_not_last(volatile u_int *count)
117 {
118 u_int old;
119
120 old = *count;
121 for (;;) {
122 KASSERT(old > 0, ("refcount %p is zero", count));
123 if (old == 1)
124 return (false);
125 if (atomic_fcmpset_int(count, &old, old - 1))
126 return (true);
127 }
128 }
129
130 #endif /* ! __SYS_REFCOUNT_H__ */
131