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audio: avoid possible deadlock regression for some AOs

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It's conceivable that ao->driver->reset() will make the audio API wait
for ao_read_data() (i.e. its audio callback) to return. Since we
recently moved the reset() call inside the same lock that ao_read_data()
acquires, this could deadlock. Whether this really happens depends on
how exactly the AO behaves. For example, ao_wasapi does not have this
problem. "Push" AOs are not affected either.

Fix by moving it outside of the lock. Assume ao->driver->start() will
not have this problem.

Could affect ao_sdl, ao_coreaudio (and similar rotten fruit AOs). I'm
unsure whether anyone experienced the problem in practice.
This commit is contained in:
wm4 2020-06-02 20:43:32 +02:00
parent 08b198aab4
commit 68ade4e5a5
1 changed files with 17 additions and 2 deletions
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19
audio/out/buffer.c
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@ -327,6 +327,7 @@ void ao_reset(struct ao *ao)
{
struct buffer_state *p = ao->buffer_state;
bool wakeup = false;
bool do_reset = false;
pthread_mutex_lock(&p->lock);
@ -334,7 +335,13 @@ void ao_reset(struct ao *ao)
mp_ring_reset(p->buffers[n]);
if (!ao->stream_silence && ao->driver->reset) {
ao->driver->reset(ao); // assumes the audio callback thread is stopped
if (ao->driver->write) {
ao->driver->reset(ao);
} else {
// Pull AOs may wait for ao_read_data() to return.
// That would deadlock if called from within the lock.
do_reset = true;
}
p->streaming = false;
}
p->paused = false;
@ -350,6 +357,9 @@ void ao_reset(struct ao *ao)
pthread_mutex_unlock(&p->lock);
if (do_reset)
ao->driver->reset(ao);
if (wakeup)
ao_wakeup_playthread(ao);
}
@ -358,6 +368,7 @@ void ao_pause(struct ao *ao)
{
struct buffer_state *p = ao->buffer_state;
bool wakeup = false;
bool do_reset = false;
pthread_mutex_lock(&p->lock);
@ -373,7 +384,8 @@ void ao_pause(struct ao *ao)
p->streaming = false;
}
} else if (ao->driver->reset) {
ao->driver->reset(ao);
// See ao_reset() why this is done outside of the lock.
do_reset = true;
p->streaming = false;
}
}
@ -383,6 +395,9 @@ void ao_pause(struct ao *ao)
pthread_mutex_unlock(&p->lock);
if (do_reset)
ao->driver->reset(ao);
if (wakeup)
ao_wakeup_playthread(ao);
}