Passing multiple objects from children to main thread

Question

i've this problem, I've a Multithreaded server running. here it's the code:

 ServerSocket serverSocket=null; // defining a server socket to listen data
         Socket clientSocket = null; // defining a client socket to send data
        final int port=8080; 
        int i=0;
        try {
            serverSocket = new ServerSocket(port); // Opening a server socket to listen for client calls
            System.out.println("Server started.");
        } catch (Exception e) {
            System.err.println("Port already in use.");
            System.exit(1);
        }

        while (true) {

            try {

                clientSocket = serverSocket.accept(); //binding server socket to client socket incoming call and accepting call
                System.out.println("Accepted connection : " + clientSocket);
                i=i+1;
                Thread t = new Thread(new newClientHandler(clientSocket, NodePRs[1]),"thread"+i); //Create a new thread to handle the single call coming from one client
                System.out.println("Thread "+t.getName()+" is starting");
                t.start(); //Starting the run method contained in newCLIENTHandler class

            } catch (Exception e) {
                System.err.println("Error in connection attempt.");
            }
            }//end while

All that i need is to let the children thread (opened every time a client request come) pass (like a function return) 4 variables when the children thread die. The newClientHandler code is this:

        public class newClientHandler implements Runnable {


     private final static int FILE_SIZE=6022386;


     private Socket clientSocket;
     private PaillierPrivateKey PrivKey;
     ServerSocket servSock;
     BigInteger[] msg = null;
     BigInteger preamble = null;
     int bytesRead;
     int current = 0;
     DataOutputStream dos = null;
     BufferedReader dis = null;
     FileOutputStream fos = null;
     BufferedOutputStream bos = null;
     int msgtype=-1;
     int num_of_rx_cnks=-1;


    public newClientHandler(Socket client, PaillierPrivateKey PR) {
        this.clientSocket = client;
        this.PrivKey = PR;

    }

//I CAN RECEIVE 3 TYPES OF MESSAGES: SHARE, THE ENCRYPTED PASSWORD, THE 4 PDMS
    public void run() {
        try{

             ObjectOutputStream oos = new ObjectOutputStream(clientSocket.getOutputStream());
             ObjectInputStream ois = new ObjectInputStream(clientSocket.getInputStream());
             preamble = (BigInteger) ois.readObject();


             System.out.println("Received Preamble is:"+preamble);
             oos.writeObject("Received preamble");
             msg =(BigInteger[]) ois.readObject();
             System.out.println("Received Message is:"+msg+"\n"+msg[0]+"\n"+msg[2]);



             String sPlain = Utilities.bigIntegerToString(preamble);
             String[] splitArr=Pattern.compile("-").split(sPlain);
             msgtype=Integer.parseInt(splitArr[0]);
             num_of_rx_cnks=Integer.parseInt(splitArr[1]);
             System.out.println("Message type: "+msgtype+"\n"+"Number of received cnks: "+num_of_rx_cnks);


             //a questo punto ho i miei 29 biginteger. Li devo sistemare uno accanto all'altro e rimettere nel file. 



             switch(msgtype){

             case 1: //Share received

                 System.out.println("Received the share");
                 for(int i=0;i<num_of_rx_cnks;i++){
                        String name = new String();
                        if(i<9){
                            name="Cyph2"+".00"+(i+1);
                        }
                        if(i>8){
                            name="Cyph2"+".0"+(i+1);
                        }
                        Utilities.newBigIntegerToFile(msg[i], name);
                    }

                    Utilities.retrieveShare(PrivKey, 2,"myShare");
                    int l, w;
                    BigInteger v, n, shares, combineSharesConstant;
                    BigInteger[]  viarray=new BigInteger[5];
                    PaillierPrivateThresholdKey[] res = null;
                    try {  
                        FileReader File= new FileReader("myShare");
                        BufferedReader buf=new BufferedReader(File);
                        String line=buf.readLine();
                        l = Integer.parseInt(line.split(":")[1]);

                        line = buf.readLine();
                        w = Integer.parseInt(line.split(":")[1]);

                        line = buf.readLine();
                        v = new BigInteger(line.split(":")[1]);

                        line = buf.readLine();
                        n = new BigInteger(line.split(":")[1]);

                        line = buf.readLine();
                        combineSharesConstant = new BigInteger(line.split(":")[1]);

                        line = buf.readLine();
                        shares = new BigInteger(line.split(":")[1]);

                        for(int i=0; i<5; i++){
                        line = buf.readLine();
                        viarray[i] = BigInteger.ZERO;
                        }

                    SecureRandom rnd = new SecureRandom();
                    PaillierPrivateThresholdKey result = new PaillierPrivateThresholdKey(n, l, combineSharesConstant, w, v, 
                            viarray, shares, 2, rnd.nextLong());//il 2 qua è il nodeID
                    }catch(IOException e){
                        System.out.println(e);
                    }
                 break;

             case 2: // Session Secret received

                 break;

             case 3: //PDM received

                 break;


             }//end switch





        }catch(IOException ioe){
            System.out.println(ioe);
        }catch(ClassNotFoundException cnfe){
            System.out.println(cnfe);
        }finally {
            try{
                  if (dis != null) dis.close();
                  if (dos != null) dos.close();
                  if (clientSocket!=null) clientSocket.close();
                }catch (IOException e){
                    System.out.println(e);
                    }
            }



        }
}

I'd like to pass l, w, v, n and so on to let my main thread do some processing. How can i modify my code to do it?

Answer 1

Use a Callable instead of a Runnable.

Bundle the 4 variables into a class and implement Callable<YourNewClass> . Run your callable with an executor and you'll get the results in a Future<YourNewClass> .