This function is called by
           - set_status
           - _update_program_stack if active program is being changed
             - thia may be launched by sensor status change.
             status lock is necessary because these happen from different
             threads.

        This does not directly change status, but adds change request
        to queue.

def _do_change_status(self, status, force=False):
        """
        This function is called by
           - set_status
           - _update_program_stack if active program is being changed
             - thia may be launched by sensor status change.
             status lock is necessary because these happen from different
             threads.

        This does not directly change status, but adds change request
        to queue.
        """
        self.system.worker_thread.put(DummyStatusWorkerTask(self._request_status_change_in_queue, status, force=force))