[issue42558] waitpid/waitid race caused by change to Popen.send_signal in Python 3.9

[STINNER Victor]

STINNER Victor <vstinner at python.org> added the comment:

The script fails with "ChildProcessError: [Errno 10] No child processes" on line:

> os.waitpid(child.pid, 0)

The line before, you call child.kill() which sends SIGKILL signal to the process. So it's likely that the process will complete (killed by SIGKILL) soon.

I don't think that it's a good idea to attempt reading the process status directly (by calling os.waitpid), since subprocess already tracks the process status.

There is the public child.poll() API which calls os.waitpid(child.pid, 0) in a safe way for you. Why not using this API?

IMO this issue is not a bug.

Note: Python 3.8 behaves differently, but it doesn't mean that calling directly os.waitpid() was a good idea in Python 3.8 and older ;-)

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nosy: +gregory.p.smith, vstinner

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