@Override
    public void registerUserProcessor(UserProcessor<?> processor) {
        UserProcessorRegisterHelper.registerUserProcessor(processor, this.userProcessors);
        // startup the processor if it registered after component startup
        if (isStarted() && !processor.isStarted()) {
            processor.startup();
        }
    }
Shutdown.
<p>
Notice:<br>
  <li>Rpc client can not be used any more after shutdown.
  <li>If you need, you should destroy it, and instantiate another one.
src/main/java/com/alipay/remoting/rpc/RpcClient.java