AnyIO commit breaks Matplotlib display in separate windows

[ianthomas23]

With the commit before the AnyIO PR on the main branch (830829f) and using ipython 8.23.0 and matplotlib 3.8.4, the displaying of Matplotlib plots in separate windows (e.g. with qt backend) using jupyter works fine. With the AnyIO commit (772dfb8) onwards the plot windows are no longer displayed.

Code to reproduce (I've been using jupyter qtconsole but jupyter lab, etc, all show the same):

%matplotlib qt
import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([1, 3, 2])

In ipython the same example works fine.

[davidbrochart]

Probably because of external event loop integration.

[ianthomas23]

enter_eventloop is only ever called if kernel.eventloop is set at startup:

ipykernel/ipykernel/kernelapp.py

Lines 732 to 736 in a7d66ae

	async def main(self):
	async with create_task_group() as tg:
	if self.kernel.eventloop:
	tg.start_soon(self.kernel.enter_eventloop)
	tg.start_soon(self.kernel.start)

If the eventloop is set later, e.g. via %matplotlib qt, it is never called.

Plus there are 7 uses of kernel.shell_stream in eventloops.py and the shell_stream was replaced with shell_port in the AnyIO changes. So evidently this code isn't covered by any ipykernel tests.