Message 122137 - Python tracker

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In-reply-to
Author	nh2
Recipients	BreamoreBoy, Rhamphoryncus, bamby, exarkun, georg.brandl, laca, movement, mstepnicki, nh2, pitrou, ross
Date	2010年11月22日.15:32:42
SpamBayes Score	6.579684e-10
Marked as misclassified	No
Message-id	<1290439967.9.0.942957453512.issue1975@psf.upfronthosting.co.za>

Content
My problem was actually related to the subprocess.Popen I use inside my threads in combination with signals. As Popen does not spawn a new thread, but a new process, it completely ignores my locks. However, it seems impossible to safely unregister signals for subprocesses. I tried using SIG_IGN in preexec_fn for Popen as well as a ignore/Popen/unignore wrapper, but both result in race conditions (for the first: if the signal arrives between fork and exec and for the second if it arrives within the wrapper). I think ignoring signals by default for everything but the main thread or process would solve this problem and make parallel programming with events in Python a lot easier. Explicit is better than implicit.

Content

My problem was actually related to the subprocess.Popen I use inside my threads in combination with signals. As Popen does not spawn a new thread, but a new process, it completely ignores my locks.
However, it seems impossible to safely unregister signals for subprocesses. I tried using SIG_IGN in preexec_fn for Popen as well as a ignore/Popen/unignore wrapper, but both result in race conditions (for the first: if the signal arrives between fork and exec and for the second if it arrives within the wrapper).
I think ignoring signals by default for everything but the main thread or process would solve this problem and make parallel programming with events in Python a lot easier.
Explicit is better than implicit.

History
Date	User	Action	Args
2010年11月22日 15:32:47	nh2	set	recipients: + nh2, georg.brandl, exarkun, Rhamphoryncus, pitrou, movement, ross, bamby, laca, mstepnicki, BreamoreBoy
2010年11月22日 15:32:47	nh2	set	messageid: <1290439967.9.0.942957453512.issue1975@psf.upfronthosting.co.za>
2010年11月22日 15:32:43	nh2	link	issue1975 messages
2010年11月22日 15:32:42	nh2	create

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