def clear_shell(self):
        """
        Unbinds the active shell service
        """
        with self._lock:
            # Clear the flag
            self._shell_event.clear()

            # Clear the readline completer
            if readline is not None:
                readline.set_completer(None)
                del self._readline_matches[:]

            if self._shell_ref is not None:
                # Release the service
                self._context.unget_service(self._shell_ref)

            self._shell_ref = None
            self._shell = None