Submit a call for future execution

        :return: future for the call execution
        :rtype: StoredFuture

def submit(self, call, *args, **kwargs):
        """
        Submit a call for future execution

        :return: future for the call execution
        :rtype: StoredFuture
        """
        future = StoredFuture(call, *args, **kwargs)
        self._queue.put(future)
        self._ensure_worker()
        return future