code.delx.au - pulseaudio/blob - src/pulsecore/once-posix.c

   1 /* $Id$ */
   2
   3 /***
   4   This file is part of PulseAudio.
   5
   6   Copyright 2006 Lennart Poettering
   7
   8   PulseAudio is free software; you can redistribute it and/or modify
   9   it under the terms of the GNU Lesser General Public License as published
  10   by the Free Software Foundation; either version 2 of the License,
  11   or (at your option) any later version.
  12
  13   PulseAudio is distributed in the hope that it will be useful, but
  14   WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16   General Public License for more details.
  17
  18   You should have received a copy of the GNU Lesser General Public License
  19   along with PulseAudio; if not, write to the Free Software
  20   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
  21   USA.
  22 ***/
  23
  24 #ifdef HAVE_CONFIG_H
  25 #include <config.h>
  26 #endif
  27
  28 #include <pthread.h>
  29
  30 #include <pulsecore/macro.h>
  31 #include <pulsecore/mutex.h>
  32
  33 #include "once.h"
  34
  35 /* Not reentrant -- how could it be? */
  36 void pa_once(pa_once_t *control, pa_once_func_t func) {
  37     pa_mutex *m;
  38
  39     pa_assert(control);
  40     pa_assert(func);
  41
  42     if (pa_atomic_load(&control->done))
  43         return;
  44
  45     pa_atomic_inc(&control->ref);
  46
  47     for (;;) {
  48
  49         if ((m = pa_atomic_ptr_load(&control->mutex))) {
  50
  51             /* The mutex is stored in locked state, hence let's just
  52              * wait until it is unlocked */
  53             pa_mutex_lock(m);
  54             pa_mutex_unlock(m);
  55             break;
  56         }
  57
  58         pa_assert_se(m = pa_mutex_new(0));
  59         pa_mutex_lock(m);
  60
  61         if (pa_atomic_ptr_cmpxchg(&control->mutex, NULL, m)) {
  62             func();
  63             pa_atomic_store(&control->done, 1);
  64             pa_mutex_unlock(m);
  65
  66             break;
  67         }
  68
  69         pa_mutex_unlock(m);
  70         pa_mutex_free(m);
  71     }
  72
  73     pa_assert(pa_atomic_load(&control->done));
  74
  75     if (pa_atomic_dec(&control->ref) <= 1) {
  76         pa_assert(pa_atomic_ptr_cmpxchg(&control->mutex, m, NULL));
  77         pa_mutex_free(m);
  78     }
  79
  80     /* Caveat: We have to make sure that the once func has completed
  81      * before returning, even if the once func is not actually
  82      * executed by us. Hence the awkward locking. */
  83 }