lib/libthread_xu/thread/thr_once.c

   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  * $DragonFly: src/lib/libthread_xu/thread/thr_once.c,v 1.3 2006/04/06 13:03:09 davidxu Exp $
  33  */
  34
  35 #include "namespace.h"
  36 #include <pthread.h>
  37 #include "un-namespace.h"
  38
  39 #include "thr_private.h"
  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 __strong_reference(_pthread_once, pthread_once);