2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org>
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
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.
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
31 #ifndef __SYS_REFCOUNT_H__
32 #define __SYS_REFCOUNT_H__
34 #include <sys/limits.h>
35 #include <machine/atomic.h>
38 #include <sys/systm.h>
41 #define KASSERT(exp, msg) /* */
45 refcount_init(volatile u_int *count, u_int value)
52 refcount_acquire(volatile u_int *count)
55 KASSERT(*count < UINT_MAX, ("refcount %p overflowed", count));
56 atomic_add_int(count, 1);
59 static __inline __result_use_check bool
60 refcount_acquire_checked(volatile u_int *count)
64 for (lcount = *count;;) {
65 if (__predict_false(lcount + 1 < lcount))
67 if (__predict_true(atomic_fcmpset_int(count, &lcount,
74 refcount_release(volatile u_int *count)
78 atomic_thread_fence_rel();
79 old = atomic_fetchadd_int(count, -1);
80 KASSERT(old > 0, ("refcount %p is zero", count));
85 * Last reference. Signal the user to call the destructor.
87 * Ensure that the destructor sees all updates. The fence_rel
88 * at the start of the function synchronized with this fence.
90 atomic_thread_fence_acq();
95 * This functions returns non-zero if the refcount was
96 * incremented. Else zero is returned.
98 * A temporary hack until refcount_* APIs are sorted out.
100 static __inline __result_use_check bool
101 refcount_acquire_if_not_zero(volatile u_int *count)
107 KASSERT(old < UINT_MAX, ("refcount %p overflowed", count));
110 if (atomic_fcmpset_int(count, &old, old + 1))
115 static __inline __result_use_check bool
116 refcount_release_if_not_last(volatile u_int *count)
122 KASSERT(old > 0, ("refcount %p is zero", count));
125 if (atomic_fcmpset_int(count, &old, old - 1))
130 #endif /* ! __SYS_REFCOUNT_H__ */