Hi,
I have a problem doing I/O in a python thread.
I want a thread to execute a command using
os.popen, read its input until the end, and
then print 'DONE' and terminate.
However, the thread hangs when it reaches
the end of the stream.
The command that I want to do is 'rsync'
which is used to transfer files between hosts.
Rsync uses ssh to transfer the data securely.
Here is a small program that demonstrates
the problem:
------START-------
#!/usr/bin/python2.3
# -*- python -*-
# This program demonstrates a case when Python locks up.
# It runs the program 'rsync' and reads its output.
# When this is done inside a thread, the program locks up
# while doing the last i.readline()
# To try the program, make sure that you can ssh into localhost
# without password prompt, and that /etc/hosts exists
#
fileToGet = '/etc/hosts'
cmd='rsync -v -e ssh localhost:%s file.txt' % fileToGet
def do():
import os
(o,i)=os.popen4 (cmd)
readAll(i)
def readAll(i):
x=i.readline()
while x:
print x
x=i.readline() # this is where the program locks up
print 'DONE'
from threading import Thread
class RunInThread(Thr ead):
def __init__(self,r un,daemon=True) :
Thread.__init__ (self)
self.setDaemon( daemon)
self.run = run
self.start()
print '\nFirst we run the command outside of a thread. This works fine.\n'
do()
print '\nNow we will run the command inside a python thread. '
print 'The program will never print DONE, nor finish.\n'
RunInThread(do, daemon=False)
-------END-------
This problem occurs with rsync, so one guess is that it
is related to the interaction with python's threads and
and rsync or ssh.
One message I google'd up mentioned that non-standard
sighandlers could be a problem when running rsync from perl,
but I have not had any luck there.
I have also tried pexpect and pty.fork as alternatives to popen,
but with no luck.
I have the same problem on both Windows and Linux platforms.
It occurs on many versions of python.
I'd be very grateful for any suggestions/hints/solutions
to this problem!
Thanks!
Lars
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