Python 3.3 hanging analysis

gistfile1.py

#/usr/lib/python3.3/subprocess.py, inside def _communicate_with_poll:

while self._fd2file:
    timeout = self._remaining_time(endtime)
    if timeout is not None and timeout < 0:
        raise TimeoutExpired(self.args, orig_timeout)
    try:
        ready = poller.poll(timeout)
    except select.error as e:
        if e.args[0] == errno.EINTR:
            continue
        raise
    self._check_timeout(endtime, orig_timeout)

    # XXX Rewrite these to use non-blocking I/O on the
    # file objects; they are no longer using C stdio!

    for fd, mode in ready:
        if mode & select.POLLOUT:
            chunk = input_view[self._input_offset :
                                self._input_offset + _PIPE_BUF]
            try:
                self._input_offset += os.write(fd, chunk)
            except OSError as e:
                if e.errno == errno.EPIPE:
                    close_unregister_and_remove(fd)
                else:
                    raise
            else:
                if self._input_offset >= len(self._input):
                    close_unregister_and_remove(fd)
        elif mode & select_POLLIN_POLLPRI:
            data = os.read(fd, 32768)
            if not data:
                close_unregister_and_remove(fd)
            self._fd2output[fd].append(data)
        else:
            # Ignore hang up or errors.
            close_unregister_and_remove(fd)

return (stdout, stderr)

###################################################
Entry for both scenario:
self.stdout.fileno() => 6
self.stderr.fileno() => 8
self._fd2file => {8: <_io.BufferedReader name=8>, 6: <_io.BufferedReader name=6>}


Normal scenario:
ready = poller.poll(timeout) => [(8, 16), (6, 17)]
close_unregister_and_remove(fd) with fd = 8
select_POLLIN_POLLPRI for fd = 6
data = b'Downloading/unpacking INITools\n ...'
self._fd2file => {6: <_io.BufferedReader name=6>}
ready = poller.poll(timeout) => [(6, 16)]
close_unregister_and_remove(fd) with fd = 6
=> DONE and test pass


Stuck scenario:
self.stdout.fileno() => 6
self.stderr.fileno() => 8
self._fd2file => {8: <_io.BufferedReader name=8>, 6: <_io.BufferedReader name=6>}

ready = poller.poll(timeout) => [(6, 1)]
select_POLLIN_POLLPRI for fd = 6
data => b'Downloading/unpacking INITools\n ...'
self._fd2file => {8: <_io.BufferedReader name=8>, 6: <_io.BufferedReader name=6>}
ready = poller.poll(timeout) => STUCK FOREVER