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once-posix.c

/* $Id: once-posix.c 1426 2007-02-13 15:35:19Z ossman $ */

/***
  This file is part of PulseAudio.

  Copyright 2006 Lennart Poettering

  PulseAudio is free software; you can redistribute it and/or modify
  it under the terms of the GNU Lesser General Public License as published
  by the Free Software Foundation; either version 2 of the License,
  or (at your option) any later version.

  PulseAudio is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License
  along with PulseAudio; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
  USA.
***/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <pthread.h>
#include <assert.h>

#include <pulsecore/mutex.h>

#include "once.h"

#define ASSERT_SUCCESS(x) do { \
    int _r = (x); \
    assert(_r == 0); \
} while(0)

static pa_mutex *global_mutex;
static pthread_once_t global_mutex_once = PTHREAD_ONCE_INIT;

static void global_mutex_once_func(void) {
    global_mutex = pa_mutex_new(0);
}

void pa_once(pa_once_t *control, pa_once_func_t func) {
    assert(control);
    assert(func);

    /* Create the global mutex */
    ASSERT_SUCCESS(pthread_once(&global_mutex_once, global_mutex_once_func));

    /* Create the local mutex */
    pa_mutex_lock(global_mutex);
    if (!control->mutex)
        control->mutex = pa_mutex_new(1);
    pa_mutex_unlock(global_mutex);

    /* Execute function */
    pa_mutex_lock(control->mutex);
    if (!control->once_value) {
        control->once_value = 1;
        func();
    }
    pa_mutex_unlock(control->mutex);

    /* Caveat: We have to make sure that the once func has completed
     * before returning, even if the once func is not actually
     * executed by us. Hence the awkward locking. */
}

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