just_run does not close event loop it creates

[akx]

If there is no running event loop, nbclient.util.just_run, as used by nbclient.util.run_sync, as used by the synchronous NotebookClient.execute() wrapper, creates a new event loop but never closes it:

nbclient/nbclient/util.py

Lines 40 to 60 in 4e99419

	def just_run(coro: Awaitable) -> Any:
	"""Make the coroutine run, even if there is an event loop running (using nest_asyncio)"""
	try:
	loop = asyncio.get_running_loop()
	except RuntimeError:
	loop = None
	if loop is None:
	had_running_loop = False
	loop = asyncio.new_event_loop()
	asyncio.set_event_loop(loop)
	else:
	had_running_loop = True
	if had_running_loop:
	# if there is a running loop, we patch using nest_asyncio
	# to have reentrant event loops
	check_ipython()
	import nest_asyncio
	nest_asyncio.apply()
	check_patch_tornado()
	return loop.run_until_complete(coro)

This could cause ResourceWarnings: jupyter/nbconvert#1856

[davidbrochart]

Thanks @akx for opening an issue.
I am experimenting with a new implementation in #250.

[akx]

Welp, just_run is no more, so I guess this was fixed in #259.