urllib hanging in thread

[Russell E. Owen]

I am having trouble with some ftp code. On some platforms it works fine 
and on others it reliably hangs.

The code uses urllib to retrieve a file in a background thread, which 
runs the following code. The diagnostic message before urllib.urlopen is 
printed, but the one after urllib.urlopen is not:

    def _getTask(self):
        try:
            self._toFile = file(self.toPath, 'wb')
            print "opening URL"
            self._fromFile = urllib.urlopen(self.fromURL)
            print "URL opened" # when hung this does not print
            self._totBytes = 
self._fromFile.info().getheader("Content-Length")
            if self._totBytes:
                self._totBytes = int(self._totBytes)
            
            self._state = Running
            
            while True:
                nextData = self._fromFile.read(8192)
                if not nextData:
                    break
                elif self._state == Aborting:
                    self._cleanup(Aborted)
                    return
                self._readBytes += len(nextData)
                self._toFile.write(nextData)
            self._cleanup(Done)
        except Exception, e:
            self._cleanup(Failed, exception = e)

However, I can only make it hang when run as part of a fairly large 
Tkinter application. The same code runs fine standalone or as part of a 
minimal Tkinter test application. The large application has a few other 
threads for communicating via TCP. In all other respects the large app 
runs fine; the ftp hangs while everything else keeps cooking along. 
Closing the TCP connection (which should stop the other threads) has no 
effect on the stalled ftp transfer.

It works fine on my MacOS X 10.3.3 box, including both the built in 
python (a variant of 2.3 with aqua Tk) and a python 2.3.3 that I built 
as a plain unix python with X11 Tk.

The code hangs on our RedHat linux boxes (python 2.3.3, dunno the linux 
version). It also hangs as a standalone MacOS X executable, which is 
especially weird since the code runs fine on the same computer before it 
gets packaged up as an application.

Any suggestions would be most appreciated.

-- Russell