[issue26741] subprocess.Popen should emit a ResourceWarning in destructor if the process is still running

[STINNER Victor]

STINNER Victor added the comment:

> One potential problem is how to provide for people who really want to let the child continue to run in the background or as a daemon without waiting for it, even if the parent exits. Perhaps a special method proc.detach() or whatever?

Maybe my heuristic to decide if ResourceWarning must be emitted is wrong.

If stdout and/or stderr is redirected to a pipe and the process is still alive when the destructor is called, it sounds more likely like a bug, because it's better to explicitly close these pipes.

If no stream is redirected, yeah, it's ok to pass the pid to a different function which will handle the child process. The risk here is not never called waitpid() to read the child exit status and so create zombi processes.

For daemons, I disagree: the daemon must use double fork, so the parent will quickly see its direct child process to exit. Ignoring the status of the first child status is a bug (we must call waitpid().

I have to think about the detach() idea and check if some applications use it, or even some parts of the stdlib.

Note: The ResourceWarning idea comes from asyncio.subprocess transport which also raises a ResourceWarning. I also had the idea when I read the issue #25942 and the old issue #12494.

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<http://bugs.python.org/issue26741>
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