How to remotely shutdown a Java RMI Server

Question

I have a very simple Java RMI Server that looks like the following:

    import java.rmi.*;
    import java.rmi.server.*;

    public class CalculatorImpl extends UnicastRemoteObject implements Calculator {

        private String mServerName;

        public CalculatorImpl(String serverName) throws RemoteException
        {
            super();
            mServerName = serverName;
        }

        public int calculate(int op1, int op2) throws RemoteException
        {
            return op1 + op2;
        }

        public void exit() throws RemoteException
        {
            try{
                Naming.unbind(mServerName);
                System.out.println("CalculatorServer exiting.");
            }
            catch(Exception e){}

            System.exit(1);
        }

        public static void main(String args[]) throws Exception
        {
            System.out.println("Initializing CalculatorServer.");

            String serverObjName = "rmi://localhost/Calculator";

            Calculator calc = new CalculatorImpl(serverObjName);

            Naming.rebind(serverObjName, calc);

            System.out.println("CalculatorServer running.");
        }
}

When I call the exit method, System.exit(1) throws the following exception:

CalculatorServer exiting.
java.rmi.UnmarshalException: Error unmarshaling return header; nested exception is:
        java.io.EOFException
        at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:203)
        at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:126)
        at CalculatorImpl_Stub.exit(Unknown Source)
        at CalculatorClient.<init>(CalculatorClient.java:17)
        at CalculatorClient.main(CalculatorClient.java:29)
Caused by: java.io.EOFException
        at java.io.DataInputStream.readByte(DataInputStream.java:243)
        at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:189)
        ... 4 more
[2]+  Exit 1                  java CalculatorImpl

What am I doing wrong in this method?

Answer 1

Actually just unregistering and immediately calling System.exit doesn't shut down cleanly. It basically breaks the connection before informing the client that the message was completed. What works is to start a small thread that shuts down the system like:

public void quit() throws RemoteException {
  System.out.println("quit");
  Registry registry = LocateRegistry.getRegistry();
  try {
    registry.unbind(_SERVICENAME);
    UnicastRemoteObject.unexportObject(this, false);
  } catch (NotBoundException e) {
    throw new RemoteException("Could not unregister service, quiting anyway", e);
  }

  new Thread() {
    @Override
    public void run() {
      System.out.print("Shutting down...");
      try {
        sleep(2000);
      } catch (InterruptedException e) {
        // I don't care
      }
      System.out.println("done");
      System.exit(0);
    }

  }.start();
}

The thread is needed to be able to let something happen in the future while still returning from the quit method.

Answer 2

In case anyone is having a similar problem, I figured out the answer myself. Here is my exit() method:

public void exit() throws RemoteException
{
    try{
        // Unregister ourself
        Naming.unbind(mServerName);

        // Unexport; this will also remove us from the RMI runtime
        UnicastRemoteObject.unexportObject(this, true);

        System.out.println("CalculatorServer exiting.");
    }
    catch(Exception e){}
}