gh-87135: Raise PythonFinalizationError when joining a blocked daemon thread by encukou · Pull Request #130402 · python/cpython (original) (raw)

What does thread.is_alive() return?

True. Threads that are already done can be joined normally.

I think the exception should not be conditional on not having a timeout specified.

In a finalizer, wouldn't it be OK to wait a bit for graceful termination (using join with a timeout), and then do some teardown regardless of whether the thread survived?
(If Python is being finalized, the thread would of course always survive -- but you might not be writing the code only for that case.)

Raising an exception would mean you skip that teardown, unless you have a try/except around join.

IOW, to me, the reasoning is not as clear-cut here as in the “hang the only Python thread that can run” case.

You can also end up with threading.join(timeout=...) calls in an infinite loop.

Well... You can even write an infinite loop without any join at all! :)
I guess I'm not trying to prevent hangs entirely, just make them easier to diagnose. IMO, a while thread.is_alive() loop is much easier to grok than an internal lock becoming un-acquirable.

I wrote the code to hang even with timeout; I'll update the PR if you still think that's the way to go.