kernel -- Slight changes to refcount_wait/_wakeup.
[dragonfly.git] / sys / sys / refcount.h
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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 * 3. Neither the name of the author nor the names of any co-contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 *
29 * $FreeBSD: src/sys/sys/refcount.h,v 1.1 2005/09/27 18:01:33 jhb Exp $
30 * $DragonFly: src/sys/sys/refcount.h,v 1.1 2008/06/26 23:06:52 dillon Exp $
31 */
32
33#ifndef __SYS_REFCOUNT_H__
34#define __SYS_REFCOUNT_H__
35
36#include <machine/atomic.h>
37
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38#define REFCNTF_WAITING 0x40000000
39
ed2fb120 40void _refcount_wait(volatile u_int *countp, const char *wstr);
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41int _refcount_release_wakeup(volatile u_int *countp);
42
5b296f84 43static __inline void
12f43c12 44refcount_init(volatile u_int *countp, u_int value)
5b296f84 45{
12f43c12 46 *countp = value;
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47}
48
49static __inline void
12f43c12 50refcount_acquire(volatile u_int *countp)
5b296f84 51{
12f43c12 52 atomic_add_acq_int(countp, 1);
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53}
54
55static __inline int
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56refcount_release(volatile u_int *countp)
57{
58 return (atomic_fetchadd_int(countp, -1) == 1);
59}
60
61/*
62 * Release a refcount and also handle waiters who have (atomically)
63 * set the REFCNTF_WAITING flag. If the flag was set the atomic op
64 * will fail (because the 'old' value we pass it is with the flag
65 * cleared). The atomic op can also fail on a race so the helper
66 * function deals with all cases.
67 *
68 * This function returns TRUE(1) on the last release and FALSE(0) otherwise.
69 */
70static __inline int
71refcount_release_wakeup(volatile u_int *countp)
72{
73 u_int n = *countp & ~REFCNTF_WAITING;
74 if (!atomic_cmpset_int(countp, n, n - 1))
75 return(_refcount_release_wakeup(countp));
76 return(n == 1);
77}
78
79/*
80 * Wait for all refs on *countp to go away.
81 *
82 * WARNING! If this function is used then all releases on countp MUST
83 * use refcount_release_wakeup() instead of refcount_release().
84 */
85static __inline void
ed2fb120 86refcount_wait(volatile u_int *countp, const char *wstr)
5b296f84 87{
12f43c12 88 if (*countp)
ed2fb120 89 _refcount_wait(countp, wstr);
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90}
91
92#endif /* ! __SYS_REFCOUNT_H__ */