xshmfence_futex.c revision ed6f5d66 
1/*
2 * Copyright © 2013 Keith Packard
3 *
4 * Permission to use, copy, modify, distribute, and sell this software and its
5 * documentation for any purpose is hereby granted without fee, provided that
6 * the above copyright notice appear in all copies and that both that copyright
7 * notice and this permission notice appear in supporting documentation, and
8 * that the name of the copyright holders not be used in advertising or
9 * publicity pertaining to distribution of the software without specific,
10 * written prior permission.  The copyright holders make no representations
11 * about the suitability of this software for any purpose.  It is provided "as
12 * is" without express or implied warranty.
13 *
14 * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
15 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
16 * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
17 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
18 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
19 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
20 * OF THIS SOFTWARE.
21 */
22
23#if HAVE_CONFIG_H
24#include "config.h"
25#endif
26
27#include "xshmfenceint.h"
28
29/**
30 * xshmfence_trigger:
31 * @f: An X fence
32 *
33 * Set @f to triggered, waking all waiters.
34 *
35 * Return value: 0 on success and -1 on error (in which case, errno
36 * will be set as appropriate).
37 **/
38int
39xshmfence_trigger(struct xshmfence *f)
40{
41	if (__sync_val_compare_and_swap(&f->v, 0, 1) == -1) {
42		atomic_store(&f->v, 1);
43		if (futex_wake(&f->v) < 0)
44			return -1;
45	}
46	return 0;
47}
48
49/**
50 * xshmfence_await:
51 * @f: An X fence
52 *
53 * Wait for @f to be triggered. If @f is already triggered, this
54 * function returns immediately.
55 *
56 * Return value: 0 on success and -1 on error (in which case, errno
57 * will be set as appropriate).
58 **/
59int
60xshmfence_await(struct xshmfence *f)
61{
62	while (__sync_val_compare_and_swap(&f->v, 0, -1) != 1) {
63		if (futex_wait(&f->v, -1)) {
64			if (errno != EWOULDBLOCK)
65				return -1;
66		}
67	}
68	return 0;
69}
70
71/**
72 * xshmfence_query:
73 * @f: An X fence
74 *
75 * Return value: 1 if @f is triggered, else returns 0.
76 **/
77int
78xshmfence_query(struct xshmfence *f)
79{
80	return atomic_fetch(&f->v) == 1;
81}
82
83/**
84 * xshmfence_reset:
85 * @f: An X fence
86 *
87 * Reset @f to untriggered. If @f is already untriggered,
88 * this function has no effect.
89 **/
90void
91xshmfence_reset(struct xshmfence *f)
92{
93	__sync_bool_compare_and_swap(&f->v, 1, 0);
94}
95