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, see <http://www.gnu.org/licenses/>.
18 ***/
19
20 #ifdef HAVE_CONFIG_H
21 #include <config.h>
22 #endif
23
24 #include <pulsecore/macro.h>
25
26 #include "once.h"
27
28 /* See http://www.hpl.hp.com/research/linux/atomic_ops/example.php4 for the
29 * reference algorithm used here. */
30
pa_once_begin(pa_once * control)31 bool pa_once_begin(pa_once *control) {
32 pa_mutex *m;
33
34 pa_assert(control);
35
36 if (pa_atomic_load(&control->done))
37 return false;
38
39 /* Caveat: We have to make sure that the once func has completed
40 * before returning, even if the once func is not actually
41 * executed by us. Hence the awkward locking. */
42
43 m = pa_static_mutex_get(&control->mutex, false, false);
44 pa_mutex_lock(m);
45
46 if (pa_atomic_load(&control->done)) {
47 pa_mutex_unlock(m);
48 return false;
49 }
50
51 return true;
52 }
53
pa_once_end(pa_once * control)54 void pa_once_end(pa_once *control) {
55 pa_mutex *m;
56
57 pa_assert(control);
58
59 pa_assert(!pa_atomic_load(&control->done));
60 pa_atomic_store(&control->done, 1);
61
62 m = pa_static_mutex_get(&control->mutex, false, false);
63 pa_mutex_unlock(m);
64 }
65
66 /* Not reentrant -- how could it be? */
pa_run_once(pa_once * control,pa_once_func_t func)67 void pa_run_once(pa_once *control, pa_once_func_t func) {
68 pa_assert(control);
69 pa_assert(func);
70
71 if (pa_once_begin(control)) {
72 func();
73 pa_once_end(control);
74 }
75 }
76