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linux-jack: fix deadlock when closing the client

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This lock causes a deadlock when freeing the JACK client while a
process callback is pending:

deactivate_jack -> locks mutex
   JACK thread -> calls jack_process_callback
   jack_process_callback -> blocks on mutex
jack_client_close -> joins JACK thread
(deadlock as the process callback never returns)

Instead, just don't lock the mutex. This is only mutexing on
creation/destruction of the JACK client. This is not necessary: the
process callback will only run after jack_activate (which is right
before the mutex is released in jack_init()), and will stop running
by the time jack_client_close returns. We don't actually need to
unregister any ports, so just call jack_client_close first thing in
deactivate_jack, which will guarantee the process callback has
completed before returning.

In fact, jack_process_callback isn't allowed to lock any mutexes or
allocate any memory at all, so this plug-in is still broken in this way
as obs_source_output_audio does that. This can cause audio xruns, as
realtime guarantees are violated. This is something that should be
fixed in the future, but at least it's not a deadlock.
This commit is contained in:
Hector Martin 2020-12-09 22:39:29 +09:00 committed by Jim
parent 5d6bca0fd2
commit 9616b79026
1 changed files with 3 additions and 10 deletions
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13
plugins/linux-jack/jack-wrapper.c
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@ -70,8 +70,6 @@ int jack_process_callback(jack_nframes_t nframes, void *arg)
if (data == 0)
return 0;
pthread_mutex_lock(&data->jack_mutex);
struct obs_source_audio out;
out.speakers = jack_channels_to_obs_speakers(data->channels);
out.samples_per_sec = jack_get_sample_rate(data->jack_client);
@ -96,8 +94,9 @@ int jack_process_callback(jack_nframes_t nframes, void *arg)
"jack_get_cycle_times error: guessing timestamp");
}
/* FIXME: this function is not realtime-safe, we should do something
* about this */
obs_source_output_audio(data->source, &out);
pthread_mutex_unlock(&data->jack_mutex);
return 0;
}
@ -164,17 +163,11 @@ void deactivate_jack(struct jack_data *data)
pthread_mutex_lock(&data->jack_mutex);
if (data->jack_client) {
jack_client_close(data->jack_client);
if (data->jack_ports != NULL) {
for (int i = 0; i < data->channels; ++i) {
if (data->jack_ports[i] != NULL)
jack_port_unregister(
data->jack_client,
data->jack_ports[i]);
}
bfree(data->jack_ports);
data->jack_ports = NULL;
}
jack_client_close(data->jack_client);
data->jack_client = NULL;
}
pthread_mutex_unlock(&data->jack_mutex);