[Bug 664920] [NEW] SRU: 100% CPU usage when calling a child process from a python script

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Scott Kitterman (kitterman):

== Impact ==

pygtk apps which handle signals busy-loop in the glib main loop
dispatch, causing 100% CPU usage after a signal is received.  This
commonly occurs when spawned child processes exit.

== TEST CASE ==

A simple testcase (pygtk-signal-testcase.py) is attached.  To trigger
the bug, run the testcase and send the process SIGCHLD.  When run with
pygtk 2.22-0ubuntu1 the test process will now consume 100% CPU.

== Regression Potential ==

PyGTK is core infrastructure, so the potential impact of a regression is
high.  However, the patch is small and clearly correct, and the file
descriptor being read from is nonblocking, so it should not cause
application hangs even if it tries to read more bytes than are there.


Original bugreport follows:
When creating a child process from a python script that uses pygtk 2.21, such subprocess.check_call(), 100% of the CPU  is used (technically, 100% of the core the python interpreter is using).

If the creation of the child processes are removed, the script runs as
expected.

According to user exarkun on the #python IRC channel, the problem may be
manifesting when the child process exits. It may be related to a bug
that was fixed in 9.10, but broken in 9.04. If that is the case, this is
the relevant bug report:
https://bugzilla.gnome.org/show_bug.cgi?id=481569

The code in which I noticed this problem is in the videometadata.py
module of Rapid Photo Downloader:
http://bazaar.launchpad.net/~dlynch3/rapid/trunk/annotate/head%3A/rapid/videometadata.py#L189

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: python-gtk2 2.21.0-0ubuntu1
ProcVersionSignature: Ubuntu 2.6.35-22.35-generic 2.6.35.4
Uname: Linux 2.6.35-22-generic x86_64
Architecture: amd64
Date: Thu Oct 21 22:51:42 2010
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release amd64 (20101007)
ProcEnviron:
 PATH=(custom, user)
 LANG=en_US.utf8
 SHELL=/bin/bash
SourcePackage: pygtk

** Affects: pygtk
     Importance: Unknown
         Status: Unknown

** Affects: pygtk (Ubuntu)
     Importance: Undecided
         Status: Confirmed


** Tags: amd64 apport-bug maverick
-- 
SRU: 100% CPU usage when calling a child process from a python script
https://bugs.launchpad.net/bugs/664920
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