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From:	zooko <zooko AT zooko DOT com>
Subject:	closing stdout in a child python process means that process doesn't receive bytes from stdin anymore.
Date:	Thu, 13 Nov 2008 06:30:10 -0700
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Folks:

When someone runs "bin/trial --reactor=select  
twisted.internet.test.test_process.ProcessTestsBuilder_PollReactor.test_ 
childConnectionLost" on cygwin, using the cygwin version of Python,  
either manually (which I've done on two cygwin installations), or  
from the twisted buildbot -- http://buildbot.twistedmatrix.com/ 
builders/cygwin-py2.5-select -- then once the child process closes  
its fd #2, it subsequently receives no further bytes from its fd #1,  
even though the parent process has written some bytes to that pipe.

I can reproduce this by running the Twisted unit tests, like this:

step 1: get twisted:

svn co svn://svn.twistedmatrix.com/svn/Twisted/trunk twisted

step 2: cd into the top-level directory, and run trial:

cd twisted && python ./bin/trial --reactor=select
twisted.internet.test.test_process.ProcessTestsBuilder_PollReactor.test_
childConnectionLost

On other platforms that cygwin (see the Twisted buildbot -- http:// 
buildbot.twistedmatrix.com/supported?branch=trunk -- then this test  
exits quickly with success. On cygwin, using cygwin python.exe, this  
test instead enter an infinite loop as the child waits to receive  
further bytes on its stdin, and the parent waits for the child to  
respond to those bytes. (This doesn't happen on cygwin with the  
standard Win32 build of python.exe, of course, anymore than it  
happens on a Windows system without cygwin installed when using that  
executable.)

I've opened a ticket about this on the twisted issue tracker as well:

http://twistedmatrix.com/trac/ticket/3529 # closing stdout in a child  
process on cygwin means that process doesn't receive bytes from stdin  
anymore. I think.

I've opened a ticket about this on the python issue tracker as well:

http://bugs.python.org/issue4295 # closing stdout in a child process  
on cygwin means that process doesn't receive bytes from stdin  
anymore. I think.



The version of the cygwin package of python is 2.5.1-2.


Regards,

Zooko
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