diff options
author | Lennart Poettering <lennart@poettering.net> | 2009-04-22 19:10:09 +0200 |
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committer | Lennart Poettering <lennart@poettering.net> | 2009-04-22 19:10:09 +0200 |
commit | ad12d7d4b020e6be225a8d6494de69d051ec7f81 (patch) | |
tree | fabaa0fd297f34891f7afd7663a7f9c28352f6bf /src/pulsecore/aupdate.c | |
parent | bb07c16b63339c934097b6a631fee36d92285511 (diff) |
memtrap,aupdate: split atomic update from memtrap into seperate aupdate framework
Diffstat (limited to 'src/pulsecore/aupdate.c')
-rw-r--r-- | src/pulsecore/aupdate.c | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/src/pulsecore/aupdate.c b/src/pulsecore/aupdate.c new file mode 100644 index 00000000..56ebb8e5 --- /dev/null +++ b/src/pulsecore/aupdate.c @@ -0,0 +1,129 @@ +/*** + This file is part of PulseAudio. + + Copyright 2009 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 2.1 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 <pulse/xmalloc.h> + +#include <pulsecore/semaphore.h> +#include <pulsecore/macro.h> +#include <pulsecore/mutex.h> + +#include "aupdate.h" + +#define MSB (1U << (sizeof(unsigned)*8U-1)) +#define WHICH(n) (!!((n) & MSB)) +#define COUNTER(n) ((n) & ~MSB) + +struct pa_aupdate { + pa_atomic_t read_lock; + pa_mutex *write_lock; + pa_semaphore *semaphore; +}; + +pa_aupdate *pa_aupdate_new(void) { + pa_aupdate *a; + + a = pa_xnew(pa_aupdate, 1); + pa_atomic_store(&a->read_lock, 0); + a->write_lock = pa_mutex_new(FALSE, FALSE); + a->semaphore = pa_semaphore_new(0); + + return a; +} + +void pa_aupdate_free(pa_aupdate *a) { + pa_assert(a); + + pa_mutex_free(a->write_lock); + pa_semaphore_free(a->semaphore); + + pa_xfree(a); +} + +unsigned pa_aupdate_read_begin(pa_aupdate *a) { + unsigned n; + + pa_assert(a); + + /* Increase the lock counter */ + n = (unsigned) pa_atomic_inc(&a->read_lock); + + /* When n is 0 we have about 2^31 threads running that all try to + * access the data at the same time, oh my! */ + pa_assert(COUNTER(n)+1 > 0); + + /* The uppermost bit tells us which data to look at */ + return WHICH(n); +} + +void pa_aupdate_read_end(pa_aupdate *a) { + unsigned n; + + pa_assert(a); + + /* Decrease the lock counter */ + n = (unsigned) pa_atomic_dec(&a->read_lock); + + /* Make sure the counter was valid */ + pa_assert(COUNTER(n) > 0); + + /* Post the semaphore */ + pa_semaphore_post(a->semaphore); +} + +unsigned pa_aupdate_write_begin(pa_aupdate *a) { + unsigned n; + + pa_assert(a); + + pa_mutex_lock(a->write_lock); + + n = (unsigned) pa_atomic_load(&a->read_lock); + + return !WHICH(n); +} + +unsigned pa_aupdate_write_swap(pa_aupdate *a) { + unsigned n; + + pa_assert(a); + + for (;;) { + n = (unsigned) pa_atomic_load(&a->read_lock); + + /* If the read counter is > 0 wait; if it is 0 try to swap the lists */ + if (COUNTER(n) > 0) + pa_semaphore_wait(a->semaphore); + else if (pa_atomic_cmpxchg(&a->read_lock, (int) n, (int) (n ^ MSB))) + break; + } + + return WHICH(n); +} + +void pa_aupdate_write_end(pa_aupdate *a) { + pa_assert(a); + + pa_mutex_unlock(a->write_lock); +} |