MQClientInstance(客户端处理包装)
start()[DefaultMQPullConsumerImpl DefaultMQPushConsumerImpl DefaultMQProducerImpl DefaultMQAdminExtImpl]
MQClientAPIImpl(通信API)



pull:
   pullAsyncImpl    PullCallback(回调）
   pullsyncImpl
   pullBlockIfNotFound  
   sendMessageBack(发送回broker)
push:注册MessageListener
   PullMessageService 
      run() pullMessage->callback->consumeMessageService——》consumeMessage（MessageListener）
      executePullRequestLater
      executePullRequestImmediately

RebalancePushImpl(run)->executePullRequestImmediately