Question

I only want one instance of my program running. But I want it to close the older ones, if they ore open.

This is in Java.

Answer 1

You can use a server socket address as an exclusive lock.

When your app starts, it will try to bind a server socket to a predefined address. If that fails, it means a previous instance of app is running and owning that address. Ping that address to tell the owner to exit.

serverSocket = new ServerSocket(localhost:8888)
if success, 
    start ServerSocketListeningThread
else
    socket = new Socket(localhost:8888)
    socket.close();
    sleep(100);
    repeat attempt of binding server socket

ServerSocketListeningThread
    serverSocket.accept();  //block until someone connects
    System.exit(); 

It’s easy to shut down your app from command line

telnet localhost 8888