[Python-bugs-list] [ python-Bugs-527783 ] popen3 hangs on windows

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Bugs item #527783, was opened at 2002-03-09 08:13
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Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Chris Withers (fresh)
Assigned to: Nobody/Anonymous (nobody)
Summary: popen3 hangs on windows

Initial Comment:
The following hangs on windows:

(i,o,e)=popen('python test.py')
result=o.read()+e.read()

...where test.py is the test.py of a Zope 3 CVS
checkout. I suspected a Zope 3 problem, but Thomas
Guettler also expereinced this in a different context:

popen3() of the python (2.1.2) which comes with zope
hangs on W2K:
 
 (stdin, stdout, stderr)=popen3('wvWare -x wvware.xml
foo.doc')
 text=stdout.read()

Then again, having seen bug #481896, I'm not sure this
is confined to windows.

Any ideas?

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>Comment By: Tim Peters (tim_one)
Date: 2002-03-10 04:19

Message:
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user_id=31435

If would help a lot if someone produced a small, self-
contained test case that reproduced the problem.  The usual 
outcome of *trying* to is the discovery that popen() on 
Windows hangs "for no identifiable reason at all".  
Example:  there's a test_popen2.py in the std Python test 
suite.  It hangs about 1 time in 200 when I run it on 
Win98SE.  There's no identifiable cause; it just hangs 
sometimes, and when it does it's always hung in the bowels 
of MS's code.  There are no races in the Python code 
driving it.

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Comment By: Darrell Gallion (dgallion)
Date: 2002-03-09 18:54

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os.read() doesn't block.
I'd expect you have to 
call os.read in a loop. 


i,o,e=os.popen3("../../python 
errXX.py")
print os.read(o.fileno(),10000), 
os.read(e.fileno(),10000)


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Comment By: Tim Peters (tim_one)
Date: 2002-03-09 13:22

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Chris, which version of Windows are you talking about?  You 
identified W2K for Thomas Guettler, but didn't say which 
version you were using.  The popen implementations are 
radically different across Windows flavors, so knowing 
which one you're using is important.

Alas, "important" doesn't necessarily imply helpful 
<wink>.  Historically, popen-on-Windows bugs don't get 
fixed, because they hit a brick wall after blame gets 
traced to MS internals.

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Comment By: Chris Withers (fresh)
Date: 2002-03-09 13:14

Message:
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So what should I use instead of e.read() ad o.read()

In fact, any chance of a replacement line for:

result=o.read()+e.read() 

? ;-)

cheers,

Chris

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Comment By: Darrell Gallion (dgallion)
Date: 2002-03-09 13:11

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Don't use e.read() 
This will try to read the entire file. Which doesn't 
make sense with a stream. Although I think this works with sockets? 


I'll look at a select solution.
Not sure how to know how many bytes to 
read after the select breaks out.

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Comment By: Darrell Gallion (dgallion)
Date: 2002-03-09 09:51

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This cuased the problem on Linux.

import os, re
files="""
file 
errXX.py
<<<<<<<<<<<<<
import sys
while 1:
    print >>sys.stderr, 
'x'
<<<<<<<<<<<<<
file runXX.py
<<<<<<<<<<<<<
import 
os
(i,o,e)=os.popen3("python errXX.py")
print 
e.read()
<<<<<<<<<<<<<
cmd python 
runXX.py
<<<<<<<<<<<<<
"""
files=re.split("<<<<<+",files)
for 
x in range(0,len(files), 2):
    cmd=files[x].split()
    
body=files[x+1]
    if cmd[0]=='file':
        
open(cmd[1],'w').write(body)
    elif cmd[0]=='cmd':
        os.system(' 
'.join(cmd[1:])+body)
    else:
        assert(0)


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