Re: [Jack-Devel] port disconnection callbacks (JackPortConnectCallback)

On Thu, Oct 9, 2014 at 8:32 AM, Stéphane Letz <[hidden]> wrote:

>
> Le 9 oct. 2014 à 13:49, Paul Davis <[hidden]> a écrit :
>
> >
> >
> > On Thu, Oct 9, 2014 at 2:55 AM, Matt Flax <[hidden]> wrote:
> >
> >
> > I understand what you are saying - the grey zone !
> > Something is disconnecting the ports. How would any object which is
> monitoring ports, such as qjackctl or JackPortMonitor know that the
> connection status has changed ?
> > Is there an alternative way to get notifications when  ports are
> disconnected ?
> >
> > they don't use a process callback.
> >
> > stephane, this behaviour seems clearly wrong to me. given that a client
> without a process callback can receive the connect/disconnect callbacks, it
> doesn't seem right that a client which has just returned non-zero from its
> process callback would simply stop receiving them. does that seem right to
> you?
>
> No, I'm not saying that… just saying the client is "deactivated"...
>
> >
> > i thought jack2 delivered all non-process callbacks in a separate thread?
> >
> Yep…
>
> So maybe we should go back to the initial question; what is the client
> supposed to do when the process callback does not return 0?
>

it is equivalent to having no process callback registered. the
documentation in the header is slightly ambgious because it describes the
behaviour of the callback rather than the registration:

/**
 * Tell the Jack server to call @a process_callback whenever there is
 * work be done, passing @a arg as the second argument.
 *
 * The code in the supplied function must be suitable for real-time
 * execution. That means that it cannot call functions that might
 * block for a long time. This includes all I/O functions (disk, TTY,
network),
 * malloc, free, printf, pthread_mutex_lock, sleep, wait, poll, select,
pthread_join,
 * pthread_cond_wait, etc, etc.
 *
 * @return 0 on success, otherwise a non-zero error code, causing JACK
 * to remove that client from the process() graph.
 */
int jack_set_process_callback (jack_client_t *client,
                   JackProcessCallback process_callback,
                   void *arg) JACK_OPTIONAL_WEAK_EXPORT;

so a client that has never called jack_set_process_callback() and a client
that did but has returned non-zero from the process callback are
semantically equivalent.


>
> Stéphane

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