Jupyter Collaboration prevents JupyterLab from being killed from the terminal

[martinRenou]

Issue

Installing jupyter_collaboration results in not being able to kill JupyterLab from the terminal.

Reproduce

1. Install jupyterlab and jupyter_collaboration
2. Create a Notebook, so that you create at least one room
3. Try to kill jupyterlab with Ctrl + C in the terminal

Attempts to fix the issue

After some investigation, it looks like this sys.exit call does not work as expected even though it properly raises a SystemExit.

One reason for sys.exit to not work can be a hanging thread or subprocess that has not been terminated.

My investigations so far have been:

• Removed the _confirm_exit thread from jupyter_server to see if that thread did not prevent from finishing
• Refactored the tasks cleanup in ypy-websockets and jupyter_collaboration
  • Refactor room and server tasks cleanup y-crdt/ypy-websocket#76
  • Refactor tasks cleanup #160
• Remove any AnyIO usage in ypy-websockets. I tried this because there seems to be an "AnyIO worker thread" thread hanging around upon termination.

None of these attempts fixed the issue. Though I think the refactor of the tasks cleanup could be good to include anyway.

[martinRenou]

I'm out of ideas for now. I feel like the "AnyIO worker thread" could be the culprit, but I don't know who creates it.

[davidbrochart]

One idea: BaseException catches all built-in exceptions, while Exception catches all built-in, non-system-exiting exceptions. I think KeyboardInterrupt is a system-exiting exception.
Maybe we catch BaseException instead of Exception somewhere, preventing it to be propagated up the stack?