RocketMQ 异步消息无法找到TOPIC No route info of this topic_org.apache.rocketmq.client.exception.mqclientexcep

异常

org.apache.rocketmq.client.exception.MQClientException: No route info of this topic, TopicTest
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操作步骤

按照RocketMQ官网的异步消息生产者中的《2.2 Send Messages Asynchronously》
创建了一个异步消息的生成者。如下:

public class AsyncProducer {
    public static void main(String[] args) throws Exception {
        //Instantiate with a producer group name.
        DefaultMQProducer producer = new DefaultMQProducer("please_rename_unique_group_name");
        // Specify name server addresses.
        producer.setNamesrvAddr("localhost:9876");
        //Launch the instance.
        producer.start();
        producer.setRetryTimesWhenSendAsyncFailed(0);
        for (int i = 0; i < 100; i++) {
                final int index = i;
                //Create a message instance, specifying topic, tag and message body.
                Message msg = new Message("TopicTest",
                    "TagA",
                    "OrderID188",
                    "Hello world".getBytes(RemotingHelper.DEFAULT_CHARSET));
                producer.send(msg, new SendCallback() {
                    @Override
                    public void onSuccess(SendResult sendResult) {
                        System.out.printf("%-10d OK %s %n", index,
                            sendResult.getMsgId());
                    }
                    @Override
                    public void onException(Throwable e) {
                        System.out.printf("%-10d Exception %s %n", index, e);
                        e.printStackTrace();
                    }
                });
        }
        //Shut down once the producer instance is not longer in use.
        producer.shutdown();
    }
}
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在我启动了namesrv、broker和consumer之后，运行该示例代码。
结果就出现了,无法找到Topic的异常。

No route info of this topic, TopicTest
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问题分析

通过

mqadmin clusterList -n 127.0.0.1:9876
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我发现broker与namesrv的连接是没有问题的。

---

然后我又在通过在mqbroker的启动参数上增加autoCreateTopicEnable=true

mqbroker -n localhost:9876 autoCreateTopicEnable=true
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同样的，问题没有解决。

默认情况下 broker会自动创建话题

---

由于是异步消息，所以我猜测是否是由于producer.shutdown() 提前关闭，导致其他异步的线程也受到影响。于是我在producer.shutdown();的上方使主线程睡眠。

感谢 @wang489687009 斧正

			...
        }
        //Shut down once the producer instance is not longer in use.
        Thread.sleep(3000);
        producer.shutdown();
    }
}
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再次运行，发现问题解决。

6          OK AC1619665D2818B4AAC283E0C4500002 
4          OK AC1619665D2818B4AAC283E0C4500004 
		   ...
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官方解决思路

通过在RocketMQ官方提供 AsyncProducer.java中我发现，它使用到了CountDownLatch来解决这个异步问题。

CountDownLatch类的三个方法

• void await() 调用这个方法的线程会被挂起，直到count值为0才继续执行。
• boolean await(long timeout, TimeUnit unit) 与await()类似，该方法需要设置超时时间，如果等待超过超时时间，则继续执行。
• countDown() 将count值减1。

通过CountDownLatch的构造器就可以创建

final CountDownLatch cntLatch = new CountDownLatch(4);
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官方代码示例如下

public class AsyncProducer {
    public static void main(
        String[] args) throws MQClientException
        , InterruptedException
        , UnsupportedEncodingException {

        DefaultMQProducer producer = new DefaultMQProducer("Jodie_Daily_test");
        producer.start();
        producer.setRetryTimesWhenSendAsyncFailed(0);

        int messageCount = 100;
        final CountDownLatch countDownLatch = new CountDownLatch(messageCount);
        for (int i = 0; i < messageCount; i++) {
            try {
                final int index = i;
                Message msg = new Message("Jodie_topic_1023",
                    "TagA",
                    "OrderID188",
                    "Hello world".getBytes(RemotingHelper.DEFAULT_CHARSET));
                producer.send(msg, new SendCallback() {
                    @Override
                    public void onSuccess(SendResult sendResult) {
                        countDownLatch.countDown();
                        System.out.printf("%-10d OK %s %n", index, sendResult.getMsgId());
                    }

                    @Override
                    public void onException(Throwable e) {
                        countDownLatch.countDown();
                        System.out.printf("%-10d Exception %s %n", index, e);
                        e.printStackTrace();
                    }
                });
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        countDownLatch.await(5, TimeUnit.SECONDS);
        producer.shutdown();
    }
}
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