import threading


def _forwardStream(in_, *outs):
    """Creates and starts a daemon thread which forwards the given input stream
    to one or more output streams. Used by the :func:`run` function to redirect
    a command's standard output/error streams to more than one destination.

    It is necessary to read the process stdout/ stderr on separate threads to
    avoid deadlocks.

    :arg in_:  Input stream
    :arg outs: Output stream(s)
    :returns:  The thread that has been started.
    """

    # not all file-likes have a mode attribute -
    # if not present, assume a string stream
    omodes = [getattr(o, 'mode', 'w') for o in outs]

    def realForward():
        for line in iter(in_.readline, b''):
            for i, o in enumerate(outs):
                if 'b' in omodes[i]: o.write(line)
                else:                o.write(line.decode('utf-8'))

    t = threading.Thread(target=realForward)
    t.daemon = True
    t.start()
    return t