thr_once.c revision 144518 
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. All advertising materials mentioning features or use of this software
14 *    must display the following acknowledgement:
15 *	This product includes software developed by John Birrell.
16 * 4. Neither the name of the author nor the names of any co-contributors
17 *    may be used to endorse or promote products derived from this software
18 *    without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 *
32 * $FreeBSD: head/lib/libthr/thread/thr_once.c 144518 2005-04-02 01:20:00Z davidxu $
33 */
34
35#include "namespace.h"
36#include <pthread.h>
37#include "un-namespace.h"
38
39#include "thr_private.h"
40
41__weak_reference(_pthread_once, pthread_once);
42
43#define ONCE_NEVER_DONE		PTHREAD_NEEDS_INIT
44#define ONCE_DONE		PTHREAD_DONE_INIT
45#define	ONCE_IN_PROGRESS	0x02
46#define	ONCE_MASK		0x03
47
48static pthread_mutex_t		once_lock = PTHREAD_MUTEX_INITIALIZER;
49static pthread_cond_t		once_cv = PTHREAD_COND_INITIALIZER;
50
51/*
52 * POSIX:
53 * The pthread_once() function is not a cancellation point. However,
54 * if init_routine is a cancellation point and is canceled, the effect
55 * on once_control shall be as if pthread_once() was never called.
56 */
57
58static void
59once_cancel_handler(void *arg)
60{
61	pthread_once_t *once_control = arg;
62
63	_pthread_mutex_lock(&once_lock);
64	once_control->state = ONCE_NEVER_DONE;
65	_pthread_mutex_unlock(&once_lock);
66	_pthread_cond_broadcast(&once_cv);
67}
68
69int
70_pthread_once(pthread_once_t *once_control, void (*init_routine) (void))
71{
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		_pthread_cleanup_push(once_cancel_handler, once_control);
87		init_routine();
88		_pthread_cleanup_pop(0);
89		_pthread_mutex_lock(&once_lock);
90		once_control->state = ONCE_DONE;
91		wakeup = 1;
92	}
93	_pthread_mutex_unlock(&once_lock);
94	if (wakeup)
95		_pthread_cond_broadcast(&once_cv);
96	return (0);
97}
98
99