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>
40 #define KASSERT(exp, msg) /* */
44 refcount_init(volatile u_int *count, u_int value)
51 refcount_acquire(volatile u_int *count)
54 KASSERT(*count < UINT_MAX, ("refcount %p overflowed", count));
55 atomic_add_int(count, 1);
59 refcount_release(volatile u_int *count)
63 atomic_thread_fence_rel();
64 old = atomic_fetchadd_int(count, -1);
65 KASSERT(old > 0, ("refcount %p is zero", count));
70 * Last reference. Signal the user to call the destructor.
72 * Ensure that the destructor sees all updates. The fence_rel
73 * at the start of the function synchronized with this fence.
75 atomic_thread_fence_acq();
80 * This functions returns non-zero if the refcount was
81 * incremented. Else zero is returned.
83 static __inline __result_use_check int
84 refcount_acquire_if_not_zero(volatile u_int *count)
90 KASSERT(old < UINT_MAX, ("refcount %p overflowed", count));
93 if (atomic_fcmpset_int(count, &old, old + 1))
98 static __inline __result_use_check int
99 refcount_release_if_not_last(volatile u_int *count)
105 KASSERT(old > 0, ("refcount %p is zero", count));
108 if (atomic_fcmpset_int(count, &old, old - 1))
113 #endif /* ! __SYS_REFCOUNT_H__ */