This function will be called when a graceful-stop is initiated.

def graceful_stop(self, signal_number=None, stack_frame=None):
        """
        This function will be called when a graceful-stop is initiated.
        """
        stop_msg = "Hard" if self.shutdown else "Graceful"
        if signal_number is None:
            self.log.info("%s stop called manually. "
                          "Shutting down.", stop_msg)
        else:
            self.log.info("%s stop called by signal #%s. Shutting down."
                          "Stack Frame: %s",
                          stop_msg, signal_number, stack_frame)
        self.shutdown = True
        self.crawler_list.stop()
        self.daemon_list.stop()
        self.thread_event.set()
        return True