Queue a transition for execution.

        :param transition: The transition

def execute(self, transition):
        """
        Queue a transition for execution.

        :param transition: The transition
        """
        self._transitions.append(transition)
        if self._thread is None or not self._thread.isAlive():
            self._thread = threading.Thread(target=self._transition_loop)
            self._thread.setDaemon(True)
            self._thread.start()