Intermittent IOPub timeout problems on windows

[akhmerov]

When running windows CI, I observe sporadic execution failures with a warning

WARNING | Timeout waiting for IOPub output.

Related reports: mwouts/jupytext#489 jupyter/jupyter-sphinx#157
There was a WIP PR against nbconvert that seemingly should fix this (jupyter/nbconvert#1183), but it was seemingly not finished nor taken over.

[SylvainCorlay]

cc @maartenbreddels since you authored the original PR.

[MSeal]

Are these test being run in parallel? jupyter/jupyter_client#487 is a known race condition with port acquisition. I haven't had to time to implement the proposed handshake changes to remedy that problem.

If the original reported issue is still occurring on Windows, the PR referenced is now quite out of date as those methods have been made async so the solution likely needs to be rewritten. I am unlikely be to able to work on taking that over / confirming it's still the source problem in the near future personally.

[akhmerov]

No, the tests are run sequentially, at least in jupyter-sphinx.