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.
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