[Jack-Devel] Using the callback free API with self-created RT-threads

Hello,

I'm currently trying to create a JACK-based backend for an already
existing audio processing software. The software creates multiple
RT-threads and at the end of each cycle hands the control to the audio
driver, which does the communication to whatever interface is chosen.
So far, nothing new... Using the callback free API, the communication
to the jack server went well, until the point where I shut down the
jack server and the jack client blocked unrecoverably in the
jack_cycle_wait() call.

Some studies of the jack2-sources showed, that jack_cycle_wait() is
waiting 0x7FFFFFFF microseconds (about 2147.4836 seconds) for the
signal to wake up, and afterwards kills the thread, if the signal
didn't arrive. I guess that it is expected, that jack_cycle_wait() is
solely called from the callback function provided by
jack_set_process_thread(). I'm guilty, because this is, what I am not
doing. Since I am already operating in a RT thread, I just call
jack_client_wait() from the thread my method is called on. Using the
JACK-provided thread would only mean to introduce yet another
synchronization point -- which by the way would be the same as in the
callback API.

Thinking about it, I don't really understand why the thread has to be
killed, after the time out. Even if jack_cycle_wait() was called from
the callback function, a return value of 0 should suffice to signal the
jack client, to please return from the function -- the thread would
close down automatically afterwards.

Also, the maximum time out duration is somewhat impractical, especially
in audio processing terms, as it leaves the system hanging with no
possibility to correctly handling any anomalies. I think the best way
here would be to leave it to the user, what time is adequate.

As a conclusion, I can't use this API, though it looked very promising,
and I will have to implement the callback way with some means of
synchronization. (Even if this was "fixed" in any way now, I need to
stay compatible with some older versions.)

But what I wanted to know is: Is this really the way the callback-free
API is supposed to work? Does anybody else see this as a problem or bug
that should be fixed?


Sincerely,
  Wolfgang Lorenz


PS: Is this the same as http://trac.jackaudio.org/ticket/27 ?

1378823732.7519_0.ltw:2, <20130910163502.3bb854de at mike>