VisClient/org/hfbk/vis/mcp/Pinger.java

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package org.hfbk.vis.mcp;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketAddress;
import java.util.*;

abstract class Pinger extends Thread {

        DatagramSocket socket;

        DatagramPacket paket = new DatagramPacket(new byte[32], 32);

        InetAddress broadcastIP;
        
        static int pingport=7779;
        
        
        public Pinger() {
                super("Pinger, port "+pingport);
                try {
                        broadcastIP=InetAddress.getByName("255.255.255.255");                   
                        socket=new DatagramSocket(pingport);
                        socket.setSoTimeout(2000);
                        socket.setBroadcast(true);                              
                } catch (Exception e1) {
                        throw new RuntimeException (e1);
                }
                start();
        }
        
        public void run() {
                
                //list keep found clients.
                LinkedList<SocketAddress> clientsFound=new LinkedList<SocketAddress>();
                
                while(true) try {
                        clientsFound.clear();
                        
                        byte[] data="PING\n".getBytes();
                        socket.send(new DatagramPacket(data,data.length, broadcastIP, VisMCP.clientport));
                        
                        while(true){ //not forever: either we got another answer or we leave via timeout
                                socket.receive(paket); 
                                String result = new String(paket.getData(), 0, paket.getLength());
                                if (result.equals("PONG\n"))
                                        clientsFound.add(paket.getSocketAddress());
                        }                                                                       
                } catch (Exception e) { //timeout, handle all answering remote sockets.
                        pinged(clientsFound);                   
                }       
        }
        
        abstract void pinged(List<SocketAddress> addresses);
}

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