thr_once.c revision 174112 
1/*
2 * Copyright (c) 1995 John Birrell <jb@cimlogic.com.au>.
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 JOHN BIRRELL 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: head/lib/libkse/thread/thr_once.c 174112 2007-11-30 17:20:29Z deischen $
30 */
31
32#include "namespace.h"
33#include <pthread.h>
34#include "un-namespace.h"
35#include "thr_private.h"
36
37LT10_COMPAT_PRIVATE(_pthread_once);
38LT10_COMPAT_DEFAULT(pthread_once);
39
40__weak_reference(_pthread_once, pthread_once);
41
42#define ONCE_NEVER_DONE		PTHREAD_NEEDS_INIT
43#define ONCE_DONE		PTHREAD_DONE_INIT
44#define	ONCE_IN_PROGRESS	0x02
45#define	ONCE_MASK		0x03
46
47static pthread_mutex_t		once_lock = PTHREAD_MUTEX_INITIALIZER;
48static pthread_cond_t		once_cv = PTHREAD_COND_INITIALIZER;
49
50/*
51 * POSIX:
52 * The pthread_once() function is not a cancellation point. However,
53 * if init_routine is a cancellation point and is canceled, the effect
54 * on once_control shall be as if pthread_once() was never called.
55 */
56
57static void
58once_cancel_handler(void *arg)
59{
60	pthread_once_t *once_control = arg;
61
62	_pthread_mutex_lock(&once_lock);
63	once_control->state = ONCE_NEVER_DONE;
64	_pthread_mutex_unlock(&once_lock);
65	_pthread_cond_broadcast(&once_cv);
66}
67
68int
69_pthread_once(pthread_once_t *once_control, void (*init_routine) (void))
70{
71	struct pthread *curthread;
72	int wakeup = 0;
73
74	if (once_control->state == ONCE_DONE)
75		return (0);
76	_pthread_mutex_lock(&once_lock);
77	while (*(volatile int *)&(once_control->state) == ONCE_IN_PROGRESS)
78		_pthread_cond_wait(&once_cv, &once_lock);
79	/*
80	 * If previous thread was canceled, then the state still
81	 * could be ONCE_NEVER_DONE, we need to check it again.
82	 */
83	if (*(volatile int *)&(once_control->state) == ONCE_NEVER_DONE) {
84		once_control->state = ONCE_IN_PROGRESS;
85		_pthread_mutex_unlock(&once_lock);
86		curthread = _get_curthread();
87		THR_CLEANUP_PUSH(curthread, once_cancel_handler, once_control);
88		init_routine();
89		THR_CLEANUP_POP(curthread, 0);
90		_pthread_mutex_lock(&once_lock);
91		once_control->state = ONCE_DONE;
92		wakeup = 1;
93	}
94	_pthread_mutex_unlock(&once_lock);
95	if (wakeup)
96		_pthread_cond_broadcast(&once_cv);
97	return (0);
98}
99
100