[Jack-Devel] Cannot callback the server in notification thread!

[Tim]

On 8/8/19 10:20 PM, Ethan Funk wrote:
> In an application I am writing, I am getting an error message out stderr 
> (see email subject), and a connection failure return result, when I try 
> to use jack_connect() from inside a jack_set_port_registration_callback 
> function, using Jack2. My goal is to have the application remember and 
> re-connect to a disconnected port if/when it "comes back." Am I going to 
> need to create a mostly sleeping thread just for port re-connections 
> attempts, or is there something obvious I am missing?
> 
> Thanks,
> Ethan...

If I understand your goal, I did this in MusE.
I called it 'persistent connections', or 'persistent ports'.

For example you can unplug a USB midi device currently
  in use by MusE as a 'Jack device', then re-plug it,
  and MusE will automatically reconnect to its ports
  as if nothing happened and you may continue playing.
(I made our 'ALSA devices' do the same thing!)
It should also work with other Jack clients.

Look in our driver/jack.cpp, at:
   static void registration_callback(...),
   static void port_connect_callback(...),
  and
   static int graph_callback(...),
   // This is called in the gui context,
   //  triggered by graph_callback()
   void JackAudioDevice::graphChanged().

It was complicated. Very. I needed to support Jack 1 and 2.
So there are a few sequences of calls and resulting
  sequences of callbacks for example that are different
  in Jack 1 and 2. Several tricks and traps. See comments.

My system relies HEAVILY on the jack port 'alias names',
  because it was pretty much the ONLY thing you can rely on,
  because the regular port names and port numbers change
  upon re-plugging. It automatically chooses which alias is
  best or falls back to the not so good canonical port name.

So, that's what it 'remembers' between device plug ins -
  simply the port alias or name text.

HTH.
Tim.