Stop / unload / cleanup hook for a server extension

[jtpio]

Is there currently a way for a server extension (that would run alongside other server extensions) to provide a stop / unload / cleanup hook, that would be called when the main server app is terminated (potentially in the stop method)?

It looks like one way to achieve this would be for an ExtensionApp to define the ExtensionApp.stop() method. Although this might be dedicated to extension apps started as standalone extensions?

As an example use case, a server extension could allocate extra resources that would need to be cleaned up when the app is stopped.

For example an ExtensionApp might want to instantiate a separate MappingKernelManager to keep a set of kernels isolated from the default kernel manager (this is currently explored in voila-dashboards/voila#41 and also discussed in #235).
Having a separate kernel manager would require calling the shutdown_all method to make sure the kernel processes are terminated.

[oliver-sanders]

Looks like the ExtensionApp now has a stop method, however, it is for shutting down the server from the extension rather than shutting down the extension from the server:

jupyter_server/jupyter_server/extension/application.py

Lines 419 to 423 in 3343101

	def stop(self):
	"""Stop the underlying Jupyter server.
	"""
	self.serverapp.stop()
	self.serverapp.clear_instance()