lib/libthr/thread/thr_once.c

   1 /*
   2  * Copyright (c) 2005, David Xu <davidxu@freebsd.org>
   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 unmodified, this list of conditions, and the following
  10  *    disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  25  *
  26  * $FreeBSD$
  27  *
  28  */
  29
  30 #include "namespace.h"
  31 #include <pthread.h>
  32 #include "un-namespace.h"
  33
  34 #include "thr_private.h"
  35
  36 __weak_reference(_pthread_once, pthread_once);
  37
  38 #define ONCE_NEVER_DONE         PTHREAD_NEEDS_INIT
  39 #define ONCE_DONE               PTHREAD_DONE_INIT
  40 #define ONCE_IN_PROGRESS        0x02
  41 #define ONCE_MASK               0x03
  42
  43 static pthread_mutex_t          _thr_once_lock = PTHREAD_MUTEX_INITIALIZER;
  44 static pthread_cond_t           _thr_once_cv = PTHREAD_COND_INITIALIZER;
  45
  46 /*
  47  * POSIX:
  48  * The pthread_once() function is not a cancellation point. However,
  49  * if init_routine is a cancellation point and is canceled, the effect
  50  * on once_control shall be as if pthread_once() was never called.
  51  */
  52
  53 static void
  54 once_cancel_handler(void *arg)
  55 {
  56         pthread_once_t *once_control = arg;
  57
  58         _pthread_mutex_lock(&_thr_once_lock);
  59         once_control->state = ONCE_NEVER_DONE;
  60         _pthread_mutex_unlock(&_thr_once_lock);
  61         _pthread_cond_broadcast(&_thr_once_cv);
  62 }
  63
  64 int
  65 _pthread_once(pthread_once_t *once_control, void (*init_routine) (void))
  66 {
  67         int wakeup = 0;
  68
  69         if (once_control->state == ONCE_DONE)
  70                 return (0);
  71         _pthread_mutex_lock(&_thr_once_lock);
  72         while (*(volatile int *)&(once_control->state) == ONCE_IN_PROGRESS)
  73                 _pthread_cond_wait(&_thr_once_cv, &_thr_once_lock);
  74         /*
  75          * If previous thread was canceled, then the state still
  76          * could be ONCE_NEVER_DONE, we need to check it again.
  77          */
  78         if (*(volatile int *)&(once_control->state) == ONCE_NEVER_DONE) {
  79                 once_control->state = ONCE_IN_PROGRESS;
  80                 _pthread_mutex_unlock(&_thr_once_lock);
  81                 _pthread_cleanup_push(once_cancel_handler, once_control);
  82                 init_routine();
  83                 _pthread_cleanup_pop(0);
  84                 _pthread_mutex_lock(&_thr_once_lock);
  85                 once_control->state = ONCE_DONE;
  86                 wakeup = 1;
  87         }
  88         _pthread_mutex_unlock(&_thr_once_lock);
  89         if (wakeup)
  90                 _pthread_cond_broadcast(&_thr_once_cv);
  91         return (0);
  92 }
  93
  94 void
  95 _thr_once_init()
  96 {
  97         _thr_once_lock = PTHREAD_MUTEX_INITIALIZER;
  98         _thr_once_cv = PTHREAD_COND_INITIALIZER;
  99 }