subprocess not killed when timeout fires

I've been using pytest-timeout for some time to catch whenever we have bad tests that just hang for a long time.
This doesn't happen very often and most of the time it happens locally and pytest-timeout saves the day.

We've been having an issue for some time when we run our tests in GitLab CI and a test ends up running for too long and then it's killed by pytest-timeout, The GitLab job hangs and eventually the GitLab runner crashes.

I debugged it today both locally and on GitLab and the issue I found is that we have a fixture where we open a server application using subprocess.Popen().
In the case where one of our tests takes too long and pytest is killed by pytest-timeout the subprocess remains open in the background.
Locally this isn't an issue because we cleanup any hanging processes at the start of our tests so they don't affect subsequent tests.
However in GitLab the job doesn't finish until all the processes are closed. Because the parent process is closed the GitLab runner isn't able to find any of the child processes and close those and everything hangs.

I'm running on Windows by the way.

So to get to my question, is there a way I can ensure that when pytest-timeout fires and kills pytest that it also kills any open subprocesses?

Thank you,

Alex

Start by tracing pytest-timeout's timeout handling and how it terminates pytest on Windows; the issue does not name a source file or test. Reproduce the subprocess.Popen scenario described in the issue, then verify that a timed-out test leaves no child process and that the GitLab job exits.