Question

I am currently developing a prototype for a game and I need a simple server to run it.
At this stage, I don’t want to invest the time learning about all the different full-featured multiplayer game servers already there (smartfox, etc…)

I know how to develop a basic Server with Threads listening on Sockets but I have ran into a roadblock. Here’s the run() function of the Thread

public void run() {
        try {
            out = new PrintWriter(mSocket1.getOutputStream(), true);
            in = new BufferedReader( new InputStreamReader( mSocket1.getInputStream() ) );
            String inputLine1 = null, outputLine;

            out.println("hello");
            out.flush();

            while( (inputLine1 = in.readLine()) != null) {
                outputLine = mGameControl.processInput(mPlayerNum, inputLine1);
                out.println(outputLine);
                out.flush();
                if(outputLine.contentEquals("bye"))
                    break;
            }

            Terminate();
        }
        catch(IOException e) { e.printStackTrace(); }
    }

Now my problem is that the thread is blocked waiting for input. I do have other similar Threads connected to other client which may result in information being dispatched to all clients…

How can I modify it so that a different Thread can interact with it and push info to the client?

Answer 1

Just write a synchronised public method which writes to your PrintWriter, and allow other threads to use it to send messages to your client. Call the same method from your read loop to avoid two threads writing at the same time.

Here’s a tested example:

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;


public class SocketTest {
    public static class Client implements Runnable {

        private final BufferedReader in;
        private final PrintWriter out;

        public Client(Socket clientSocket) throws IOException {
            out = new PrintWriter(clientSocket.getOutputStream(), true);
            in = new BufferedReader( new InputStreamReader( clientSocket.getInputStream() ) );
        }

        public void run() {
            send("Hello");
            String inputLine1 = null, outputLine;
            try {
                while( (inputLine1 = in.readLine()) != null) {
                    outputLine = inputLine1.toLowerCase();
                    System.out.println(inputLine1);
                    send(outputLine);
                    if(outputLine.contentEquals("bye"))
                        break;
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        public synchronized void send(String message) {
            out.println(message);
            out.flush();
        }
    }
    public static void main(String[] args) throws IOException, InterruptedException {
        ServerSocket s = new ServerSocket(5050);
        Socket clientSocket = s.accept();
        Client client = new Client(clientSocket);
        Thread clientThread = new Thread(client);
        clientThread.start();
        int i = 1;
        while (true) {
            Thread.sleep(1000);
            client.send("Tick " + (i++));
        }
    }

}