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There was a race in the existing code that could cause the pa_once code to be run twice, see: http://lists.freedesktop.org/archives/pulseaudio-discuss/2012-April/013354.html Therefore the existing implementation was rewritten to instead look like the reference implementation here: http://www.hpl.hp.com/research/linux/atomic_ops/example.php4 Signed-off-by: David Henningsson <david.henningsson@canonical.com>
77 lines
2 KiB
C
77 lines
2 KiB
C
/***
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This file is part of PulseAudio.
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Copyright 2006 Lennart Poettering
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PulseAudio is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published
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by the Free Software Foundation; either version 2.1 of the License,
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or (at your option) any later version.
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PulseAudio is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with PulseAudio; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
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USA.
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***/
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#ifdef HAVE_CONFIG_H
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#include <config.h>
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#endif
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#include <pulsecore/macro.h>
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#include "once.h"
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/* See http://www.hpl.hp.com/research/linux/atomic_ops/example.php4 for the
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* reference algorithm used here. */
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pa_bool_t pa_once_begin(pa_once *control) {
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pa_mutex *m;
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pa_assert(control);
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if (pa_atomic_load(&control->done))
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return FALSE;
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/* Caveat: We have to make sure that the once func has completed
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* before returning, even if the once func is not actually
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* executed by us. Hence the awkward locking. */
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m = pa_static_mutex_get(&control->mutex, FALSE, FALSE);
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pa_mutex_lock(m);
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if (pa_atomic_load(&control->done)) {
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pa_mutex_unlock(m);
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return FALSE;
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}
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return TRUE;
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}
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void pa_once_end(pa_once *control) {
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pa_mutex *m;
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pa_assert(control);
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pa_assert(!pa_atomic_load(&control->done));
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pa_atomic_store(&control->done, 1);
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m = pa_static_mutex_get(&control->mutex, FALSE, FALSE);
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pa_mutex_unlock(m);
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}
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/* Not reentrant -- how could it be? */
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void pa_run_once(pa_once *control, pa_once_func_t func) {
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pa_assert(control);
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pa_assert(func);
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if (pa_once_begin(control)) {
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func();
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pa_once_end(control);
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}
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}
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