fb930e8f47
when the surround bus is removed, it (probably erroneously) causes changes to the I/O routing for the auditioner, which will be delivered to anyone who cares via an RCConfiguration ParameterChanged signal. This will be emitted from a non-GUI thread, and so will not be handled synchronously. The GUI thread will first handle the notification that the surround bus was deleted, and that will include deleting the MixerStrip for the surround bus. But another call_slot() request will be pending to notify the now-deleted MixerStrip about the auditioner change. Adding invalidator() calls ensures that the deletion of the MixerStrip removes all of these pending call_slot() requests.
Please see the Ardour web site at https://ardour.org/ for all documentation..
For information on building ardour:
https://ardour.org/development.html