thr_once.c revision 172695 
1/*
2 * Copyright (c) 2005, David Xu <davidxu@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 unmodified, this list of conditions, and the following
10 *    disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 *
26 * $FreeBSD: head/lib/libthr/thread/thr_once.c 172695 2007-10-16 07:46:15Z davidxu $
27 *
28 */
29
30#include "namespace.h"
31#include <pthread.h>
32#include "un-namespace.h"
33
34#include "thr_private.h"
35
36__weak_reference(_pthread_once, pthread_once);
37
38#define ONCE_NEVER_DONE		PTHREAD_NEEDS_INIT
39#define ONCE_DONE		PTHREAD_DONE_INIT
40#define	ONCE_IN_PROGRESS	0x02
41#define	ONCE_MASK		0x03
42
43static pthread_mutex_t		_thr_once_lock = PTHREAD_MUTEX_INITIALIZER;
44static pthread_cond_t		_thr_once_cv = PTHREAD_COND_INITIALIZER;
45
46/*
47 * POSIX:
48 * The pthread_once() function is not a cancellation point. However,
49 * if init_routine is a cancellation point and is canceled, the effect
50 * on once_control shall be as if pthread_once() was never called.
51 */
52
53static void
54once_cancel_handler(void *arg)
55{
56	pthread_once_t *once_control = arg;
57
58	_pthread_mutex_lock(&_thr_once_lock);
59	once_control->state = ONCE_NEVER_DONE;
60	_pthread_mutex_unlock(&_thr_once_lock);
61	_pthread_cond_broadcast(&_thr_once_cv);
62}
63
64int
65_pthread_once(pthread_once_t *once_control, void (*init_routine) (void))
66{
67	struct pthread *curthread;
68	int wakeup = 0;
69
70	if (once_control->state == ONCE_DONE)
71		return (0);
72	_pthread_mutex_lock(&_thr_once_lock);
73	while (*(volatile int *)&(once_control->state) == ONCE_IN_PROGRESS)
74		_pthread_cond_wait(&_thr_once_cv, &_thr_once_lock);
75	/*
76	 * If previous thread was canceled, then the state still
77	 * could be ONCE_NEVER_DONE, we need to check it again.
78	 */
79	if (*(volatile int *)&(once_control->state) == ONCE_NEVER_DONE) {
80		once_control->state = ONCE_IN_PROGRESS;
81		_pthread_mutex_unlock(&_thr_once_lock);
82		curthread = _get_curthread();
83		THR_CLEANUP_PUSH(curthread, once_cancel_handler, once_control);
84		init_routine();
85		THR_CLEANUP_POP(curthread, 0);
86		_pthread_mutex_lock(&_thr_once_lock);
87		once_control->state = ONCE_DONE;
88		wakeup = 1;
89	}
90	_pthread_mutex_unlock(&_thr_once_lock);
91	if (wakeup)
92		_pthread_cond_broadcast(&_thr_once_cv);
93	return (0);
94}
95
96void
97_thr_once_init()
98{
99	_thr_once_lock = PTHREAD_MUTEX_INITIALIZER;
100	_thr_once_cv = PTHREAD_COND_INITIALIZER;
101}
102