pytest-xdist sometimes deadlocks/fails to terminate on Python 3.8, Linux

[jbarlow83]

I've found that on Linux, pytest-xdist will sometimes timeout when it has (probably) completed all tests for Python 3.8, it will continue to run indefinitely as if deadlocked. Equivalent tests on older Pythons work fine.

It is, unfortunately, a lengthy test suite.
github.com/jbarlow83/OCRmyPDF

The test suite in question passes using pytest -n0.

This has been confirmed on Fedora Rawhide and Ubuntu 18.04. I can also confirm the issue does not occur on Python 3.8 with Windows. Not tested on macOS.

Here is a run of the test suite showing Windows and Linux all working except for Python 3.8 on Linux:
https://dev.azure.com/jim0585/ocrmypdf/_build/results?buildId=173&view=results

There's a decent chance this is a Python 3.8 internal bug too, but I figured I'd start here because you probably better ideas how to test this.