[Bf-python] Remove a modal handler from the window manager

["Martin Bürbaum"]

Dan Eicher <dan at trollwerks.org> wrote:

> Somewhere in VIEW3D_OT_display_measurements there needs to be a check
> for canceling the drawing operation which then calls:
> 
> ...region.callback_remove(self._handle)
> 
> -- perhaps in modal() which calls a dedicated function to loop over
> all the windows/regions and clean this stuff up.

Ok, after some investigation I've found out that I can not remove the callback in modal(). At the time the add-on is unregistered the modal handler doesn't run anymore.

And if I use e.g. __del__ I have the wrong context and _handle is not set. :-(
Same problem if I use execute/invoke from anywhere in the code.
	
Furthermore I have searched for other, similar implementations and e.g. the space_view3d_screencast_keys script does not handle unregistering as well. There might be no display anymore, but the callback draw_callback_px() is still running.
So at least I know I'm not the only one with this exact problem.

The example implementations I've found remove the callback before unregistering, so the issue doesn't pop up there.

Cheers,
Martin