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Date: Tue, 3 Jan 2012 00:09:14 +0100
From: =?UTF-8?B?SsOpcsO0bWU=?= <jerome@jolimont.fr>
To: python-list@python.org
Subject: Avoid race condition with Popen.send_signal
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:18355

Hi all.

When a subprocess is running, it can be sent a signal with the send_signal
method :

process =3D Popen( args)
process.send_signal(signal.SIGINT)

If the SIGINT is sent while the process has already finished, an error is
raised :=20

  File "/usr/lib/python2.7/subprocess.py", line 1457, in send_signal
    os.kill(self.pid, sig)
OSError: [Errno 3] Aucun processus de ce type

To avoid this, I can check that the process is still alive :

process =3D Popen( args)
process.poll()
if (None =3D=3D process.returncode):
    process.send_signal(signal.SIGINT)

It makes safer, but there is still an issue if the process ends between
poll() and send_signal().

What is the clean way to avoid this race condition ?

Should I use try/except to catch the error or is there a more elegant way to
go ?

Thanks.

--=20
J=C3=A9r=C3=B4me