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This article introduces the relevant knowledge of "MQ underlying class MQClientInstance and ProcessQueue analysis". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Cornerstone MQClientInstance

The member variables of the DefaultMQProducerImpl, DefaultMQPullConsumerImpl, and DefaultMQPushConsumerImpl objects all contain the same member object:

Private MQClientInstance mQClientFactory;this.mQClientFactory = MQClientManager.getInstance () .getAndCreateMQClientInstance (this.defaultMQPushConsumer, this.rpcHook)

The MQClientInstance functions are as follows:

MQClientInstance is responsible for maintaining heartbeat by communicating with NameServer and obtaining Broker address according to Topic

MQClientInstance is responsible for communicating with Broker to send and receive messages and ReBalance.

In general, a production side or consumer side of RocketMQ, or a JVM process with only one MQClientInstance instance is sufficient. If you do not manually set it through setInstanceName, one or more Consumer or Producer layers created at this time all use the same MQClientInstance instance (the default name is "DEFAULT").

However, in some cases, only one MQClientInstance object is not enough. For example, a Java program needs to connect two MQ clusters, consume from one cluster and send it to another cluster, while a MQClientInstance object cannot support this scenario. In this case, you must manually specify a different InstanceName, and two MQClientInstance objects will be created at the bottom.

Public class MQClientManager {private static MQClientManager instance = new MQClientManager (); private AtomicInteger factoryIndexGenerator = new AtomicInteger (); private ConcurrentMap factoryTable = new ConcurrentHashMap ()

Generation rules for ClientId:

If there are multiple services integrated with MQ clients on the same machine, the process ID

MessageQueue's snapshot class ProcessQueue on the client side

Path: org.apache.rocketmq.client.impl.consumer

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