refcount.h revision 331722 
1/*-
2 * Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD: stable/11/sys/sys/refcount.h 331722 2018-03-29 02:50:57Z eadler $
27 */
28
29#ifndef __SYS_REFCOUNT_H__
30#define __SYS_REFCOUNT_H__
31
32#include <sys/limits.h>
33#include <machine/atomic.h>
34
35#ifdef _KERNEL
36#include <sys/systm.h>
37#else
38#define	KASSERT(exp, msg)	/* */
39#endif
40
41static __inline void
42refcount_init(volatile u_int *count, u_int value)
43{
44
45	*count = value;
46}
47
48static __inline void
49refcount_acquire(volatile u_int *count)
50{
51
52	KASSERT(*count < UINT_MAX, ("refcount %p overflowed", count));
53	atomic_add_int(count, 1);
54}
55
56static __inline int
57refcount_release(volatile u_int *count)
58{
59	u_int old;
60
61	atomic_thread_fence_rel();
62	old = atomic_fetchadd_int(count, -1);
63	KASSERT(old > 0, ("negative refcount %p", count));
64	if (old > 1)
65		return (0);
66
67	/*
68	 * Last reference.  Signal the user to call the destructor.
69	 *
70	 * Ensure that the destructor sees all updates.  The fence_rel
71	 * at the start of the function synchronized with this fence.
72	 */
73	atomic_thread_fence_acq();
74	return (1);
75}
76
77#endif	/* ! __SYS_REFCOUNT_H__ */
78