From b7567f23fbd63cf0db904accedc7e1eff6f9f300 Mon Sep 17 00:00:00 2001 From: Hector Martin Date: Wed, 9 Dec 2020 22:39:29 +0900 Subject: [PATCH] linux-jack: fix deadlock when closing the client 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. --- plugins/linux-jack/jack-wrapper.c | 13 +++---------- 1 file changed, 3 insertions(+), 10 deletions(-) diff --git a/plugins/linux-jack/jack-wrapper.c b/plugins/linux-jack/jack-wrapper.c index 16a341974..d9bba60cd 100644 --- a/plugins/linux-jack/jack-wrapper.c +++ b/plugins/linux-jack/jack-wrapper.c @@ -64,8 +64,6 @@ 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); @@ -83,8 +81,9 @@ int jack_process_callback(jack_nframes_t nframes, void *arg) out.timestamp = os_gettime_ns() - jack_frames_to_time(data->jack_client, nframes); + /* 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; } @@ -151,17 +150,11 @@ 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);