2 This file is part of PulseAudio.
4 Copyright 2009 Lennart Poettering
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
8 published by the Free Software Foundation; either version 2.1 of the
9 License, or (at your option) any later version.
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.
16 You should have received a copy of the GNU Lesser General Public
17 License along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
24 #include <pulse/xmalloc.h>
26 #include <pulsecore/semaphore.h>
27 #include <pulsecore/macro.h>
28 #include <pulsecore/mutex.h>
32 #define MSB (1U << (sizeof(unsigned)*8U-1))
33 #define WHICH(n) (!!((n) & MSB))
34 #define COUNTER(n) ((n) & ~MSB)
37 pa_atomic_t read_lock;
39 pa_semaphore *semaphore;
43 pa_aupdate *pa_aupdate_new(void) {
46 a = pa_xnew(pa_aupdate, 1);
47 pa_atomic_store(&a->read_lock, 0);
48 a->write_lock = pa_mutex_new(false, false);
49 a->semaphore = pa_semaphore_new(0);
54 void pa_aupdate_free(pa_aupdate *a) {
57 pa_mutex_free(a->write_lock);
58 pa_semaphore_free(a->semaphore);
63 unsigned pa_aupdate_read_begin(pa_aupdate *a) {
68 /* Increase the lock counter */
69 n = (unsigned) pa_atomic_inc(&a->read_lock);
71 /* When n is 0 we have about 2^31 threads running that all try to
72 * access the data at the same time, oh my! */
73 pa_assert(COUNTER(n)+1 > 0);
75 /* The uppermost bit tells us which data to look at */
79 void pa_aupdate_read_end(pa_aupdate *a) {
84 /* Decrease the lock counter */
85 n = (unsigned) pa_atomic_dec(&a->read_lock);
87 /* Make sure the counter was valid */
88 pa_assert(COUNTER(n) > 0);
90 /* Post the semaphore */
91 pa_semaphore_post(a->semaphore);
94 unsigned pa_aupdate_write_begin(pa_aupdate *a) {
99 pa_mutex_lock(a->write_lock);
101 n = (unsigned) pa_atomic_load(&a->read_lock);
108 unsigned pa_aupdate_write_swap(pa_aupdate *a) {
114 n = (unsigned) pa_atomic_load(&a->read_lock);
116 /* If the read counter is > 0 wait; if it is 0 try to swap the lists */
118 pa_semaphore_wait(a->semaphore);
119 else if (pa_atomic_cmpxchg(&a->read_lock, (int) n, (int) (n ^ MSB)))
128 void pa_aupdate_write_end(pa_aupdate *a) {
132 pa_aupdate_write_swap(a);
134 pa_mutex_unlock(a->write_lock);