Message 135026 - Python tracker

> Under what circumstances do we expect a ProcessPoolExecutor child
> process to be killed outside of the control of the
> ProcessPoolExecutor?

Killed by the user, or by an automatic device (such as the Linux OOM
killer), or crashed.

> If the user kills a child then maybe all we want to do is raise an
> exception rather than deadlock as a convenience.

That's what the patch does, roughly.