RocketMQ消息队列重新分配是由RebalancService线程来实现，一个MQClientinstance持有一个RebalanceService的实现，并随着MQClientInstance的启动而启动。我们看下下面的代码

位置：MQClientInstance:start方法

 public void start() throws MQClientException {synchronized (this) {switch (this.serviceState) {case CREATE_JUST:this.serviceState = ServiceState.START_FAILED;// If not specified,looking address from name serverif (null == this.clientConfig.getNamesrvAddr()) {this.mQClientAPIImpl.fetchNameServerAddr();}// Start request-response channelthis.mQClientAPIImpl.start();// Start various schedule tasksthis.startScheduledTask();// Start pull servicethis.pullMessageService.start();