thr_once.c revision 119928 
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/libkse/thread/thr_once.c 119928 2003-09-09 22:38:12Z davidxu $
33 */
34#include "namespace.h"
35#include <pthread.h>
36#include "un-namespace.h"
37#include "thr_private.h"
38
39__weak_reference(_pthread_once, pthread_once);
40
41#define ONCE_NEVER_DONE		PTHREAD_NEEDS_INIT
42#define ONCE_DONE		PTHREAD_DONE_INIT
43#define	ONCE_IN_PROGRESS	0x02
44#define	ONCE_MASK		0x03
45
46static pthread_mutex_t		once_lock = PTHREAD_MUTEX_INITIALIZER;
47static pthread_cond_t		once_cv = PTHREAD_COND_INITIALIZER;
48
49/*
50 * POSIX:
51 * The pthread_once() function is not a cancellation point. However,
52 * if init_routine is a cancellation point and is canceled, the effect
53 * on once_control shall be as if pthread_once() was never called.
54 */
55
56static void
57once_cancel_handler(void *arg)
58{
59	pthread_once_t *once_control = arg;
60
61	_pthread_mutex_lock(&once_lock);
62	once_control->state = ONCE_NEVER_DONE;
63	_pthread_mutex_unlock(&once_lock);
64	_pthread_cond_broadcast(&once_cv);
65}
66
67int
68_pthread_once(pthread_once_t *once_control, void (*init_routine) (void))
69{
70	int wakeup = 0;
71
72	if (once_control->state == ONCE_DONE)
73		return (0);
74	_pthread_mutex_lock(&once_lock);
75	while (*(volatile int *)&(once_control->state) == ONCE_IN_PROGRESS)
76		_pthread_cond_wait(&once_cv, &once_lock);
77	/*
78	 * If previous thread was canceled, then the state still
79	 * could be ONCE_NEVER_DONE, we need to check it again.
80	 */
81	if (*(volatile int *)&(once_control->state) == ONCE_NEVER_DONE) {
82		once_control->state = ONCE_IN_PROGRESS;
83		_pthread_mutex_unlock(&once_lock);
84		_pthread_cleanup_push(once_cancel_handler, once_control);
85		init_routine();
86		_pthread_cleanup_pop(0);
87		_pthread_mutex_lock(&once_lock);
88		once_control->state = ONCE_DONE;
89		wakeup = 1;
90	}
91	_pthread_mutex_unlock(&once_lock);
92	if (wakeup)
93		_pthread_cond_broadcast(&once_cv);
94	return (0);
95}
96
97