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

   1 /***
   2   This file is part of PulseAudio.
   3
   4   Copyright 2006 Lennart Poettering
   5
   6   PulseAudio is free software; you can redistribute it and/or modify
   7   it under the terms of the GNU Lesser General Public License as published
   8   by the Free Software Foundation; either version 2.1 of the License,
   9   or (at your option) any later version.
  10
  11   PulseAudio is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with PulseAudio; if not, write to the Free Software
  18   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
  19   USA.
  20 ***/
  21
  22 #ifdef HAVE_CONFIG_H
  23 #include <config.h>
  24 #endif
  25
  26 #include <pulsecore/macro.h>
  27
  28 #include "once.h"
  29
  30 /* See http://www.hpl.hp.com/research/linux/atomic_ops/example.php4 for the
  31  * reference algorithm used here. */
  32
  33 bool pa_once_begin(pa_once *control) {
  34     pa_mutex *m;
  35
  36     pa_assert(control);
  37
  38     if (pa_atomic_load(&control->done))
  39         return false;
  40
  41     /* Caveat: We have to make sure that the once func has completed
  42      * before returning, even if the once func is not actually
  43      * executed by us. Hence the awkward locking. */
  44
  45     m = pa_static_mutex_get(&control->mutex, false, false);
  46     pa_mutex_lock(m);
  47
  48     if (pa_atomic_load(&control->done)) {
  49         pa_mutex_unlock(m);
  50         return false;
  51     }
  52
  53     return true;
  54 }
  55
  56 void pa_once_end(pa_once *control) {
  57     pa_mutex *m;
  58
  59     pa_assert(control);
  60
  61     pa_assert(!pa_atomic_load(&control->done));
  62     pa_atomic_store(&control->done, 1);
  63
  64     m = pa_static_mutex_get(&control->mutex, false, false);
  65     pa_mutex_unlock(m);
  66 }
  67
  68 /* Not reentrant -- how could it be? */
  69 void pa_run_once(pa_once *control, pa_once_func_t func) {
  70     pa_assert(control);
  71     pa_assert(func);
  72
  73     if (pa_once_begin(control)) {
  74         func();
  75         pa_once_end(control);
  76     }
  77 }