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: src/lib/libpthread/thread/thr_once.c,v 1.9 2003/09/09 22:38:12 davidxu Exp $
33  * $DragonFly: src/lib/libthread_xu/thread/thr_once.c,v 1.1 2005/02/01 12:38:27 davidxu Exp $
34  */
35 
36 #include <pthread.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 
46 static pthread_mutex_t		once_lock = PTHREAD_MUTEX_INITIALIZER;
47 static 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 
56 static void
57 once_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 
67 int
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