How to use the dramatiq.common.iter_queue function in dramatiq

def handle_delayed_messages(self):
        """Enqueue any delayed messages whose eta has passed.
        """
        for eta, message in iter_queue(self.delay_queue):
            if eta > current_millis():
                self.delay_queue.put((eta, message))
                self.delay_queue.task_done()
                break

            queue_name = q_name(message.queue_name)
            new_message = message.copy(queue_name=queue_name)
            del new_message.options["eta"]

            self.broker.enqueue(new_message)
            self.post_process_message(message)
            self.delay_queue.task_done()

self.logger.debug("Stopping workers...")
        for thread in self.workers:
            thread.stop()

        join_all(self.workers, timeout)
        self.logger.debug("Workers stopped.")
        self.logger.debug("Stopping consumers...")
        for thread in self.consumers.values():
            thread.stop()

        join_all(self.consumers.values(), timeout)
        self.logger.debug("Consumers stopped.")

        self.logger.debug("Requeueing in-memory messages...")
        messages_by_queue = defaultdict(list)
        for _, message in iter_queue(self.work_queue):
            messages_by_queue[message.queue_name].append(message)

        for queue_name, messages in messages_by_queue.items():
            try:
                self.consumers[queue_name].requeue_messages(messages)
            except ConnectionError:
                self.logger.warning("Failed to requeue messages on queue %r.", queue_name, exc_info=True)
        self.logger.debug("Done requeueing in-progress messages.")

        self.logger.debug("Closing consumers...")
        for consumer in self.consumers.values():
            consumer.close()

        self.logger.debug("Consumers closed.")
        self.broker.emit_after("worker_shutdown", self)
        self.logger.info("Worker has been shut down.")

def close(self):
        """Close this consumer thread and its underlying connection.
        """
        try:
            if self.consumer:
                self.requeue_messages(m for _, m in iter_queue(self.delay_queue))
                self.consumer.close()
        except ConnectionError:
            pass

def flush(self, queue_name):
        """Drop all the messages from a queue.

        Parameters:
          queue_name(str): The queue to flush.
        """
        for _ in iter_queue(self.queues[queue_name]):
            self.queues[queue_name].task_done()