threads concurrency problem

[naved momin]

i have code a chat server and a client with 2 threads in each in server and 2 for client
1 thread will start writing and other thread of client will start listening to the server thread
when this both threads finish the two other thread comes into picture
where 1 server thread is listening for the client and other client thread in writing the message to the server

but my problem is with concurency because when i write in server it appears in client but when i write in client it is not visible to the server unless and until server writes another message
so can you guyz help me this is first time my app contains multithreads
please copy this code and test in your machine for better understanding
server code

package chatserver;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;

public class ChatServer implements Runnable {

    BufferedReader read;
    PrintWriter write;
    ServerSocket serversocket;
    Socket socket;

    public synchronized  void run() {
        go();
    }

    class ClientHandler implements Runnable
{
    Socket socket;
    BufferedReader read;

    public ClientHandler(Socket socket) {
                    try {
                this.socket = socket;
              read = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            } catch (IOException ex) {
                Logger.getLogger(ChatServer.class.getName()).log(Level.SEVERE, null, ex);
            }
    }

    public synchronized void run() {

        try {
            String cmsg ;
            while((cmsg = read.readLine() ) != null )
            System.out.println(cmsg);
                try {
                    Thread.sleep(100);
                } catch (InterruptedException ex) {
                    Logger.getLogger(ChatServer.class.getName()).log(Level.SEVERE, null, ex);
                }
        } catch (IOException ex) {
            Logger.getLogger(ClientHandler.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

    synchronized void go()
    {
        try {
                serversocket = new ServerSocket(9000);
            } catch (IOException ex) {
                Logger.getLogger(ChatServer.class.getName()).log(Level.SEVERE, null, ex);
            }
        while(true)
        {
            try {
            socket = serversocket.accept();
            write = new PrintWriter(socket.getOutputStream());
            System.out.println("enter your message");
            read = new BufferedReader(new InputStreamReader(System.in));
            String smsg = read.readLine();
            System.out.println("msg " + smsg);
            write.println(smsg);
            write.flush();
            Thread t = new Thread(new ClientHandler(socket));
            t.start();
        }
        catch(IOException ex) {
            Logger.getLogger(ChatServer.class.getName()).log(Level.SEVERE, null, ex);
            System.out.println("fail");
        }
    }
    }
    public static void main(String[] args) {
        // TODO code application logic here
        Thread t = new Thread(new ChatServer());
        t.start();
    }
}

client code

package chatserver;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.logging.Level;
import java.util.logging.Logger;

 class ServerHandler implements Runnable
    {
        Socket sock;
        BufferedReader read;
        PrintWriter write;

        public synchronized void run() {
         
          while(true)
          {
            try {
                sock = new Socket("127.0.0.1", 9000);
                read = new BufferedReader(new InputStreamReader(sock.getInputStream()));
                String smsg = read.readLine();
                System.out.println(smsg);
                try {
                    Thread.sleep(100);
                } catch (InterruptedException ex) {
                    Logger.getLogger(ServerHandler.class.getName()).log(Level.SEVERE, null, ex);
                }
            } catch (UnknownHostException ex) {
                Logger.getLogger(ChatClient.class.getName()).log(Level.SEVERE, null, ex);
            } catch (IOException ex) {
                Logger.getLogger(ChatClient.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
     }
}

public class ChatClient implements Runnable {

    PrintWriter write ;
    BufferedReader read;
    Socket socket;

    synchronized void go()
    {
        while(true)
        {
        try {
            socket = new Socket("127.0.01", 9000);
            write = new PrintWriter(socket.getOutputStream() , true);
            System.out.println("enter your message");
            read = new BufferedReader(new InputStreamReader(System.in));
            String msg = read.readLine();
            write.println(msg);
            write.flush();
        } catch (IOException ex) {
            Logger.getLogger(ChatClient.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    }
    
    public static void main(String[] args) {
        // TODO code application logic here

        Thread t = new Thread(new ServerHandler());
        t.start();
        Thread job = new Thread(new ChatClient());
        job.start();
    }

    public synchronized  void run() {
        go();
    }
}

[Rohan Dhapodkar]

naved momin wrote:

                socket = serversocket.accept();  
                write = new PrintWriter(socket.getOutputStream());  
                System.out.println("enter your message");  
                read = new BufferedReader(new InputStreamReader(System.in));  
                String smsg = read.readLine();  
                System.out.println("msg " + smsg);  
                write.println(smsg);  
                write.flush();  
                Thread t = new Thread(new ClientHandler(socket));  
                t.start();

This is issue with go() method of ChatServer, where you are writing to socket first and then creating read thread. Reorder your code and it will work.

                socket = serversocket.accept(); 
                Thread t = new Thread(new ClientHandler(socket));  
                t.start();
                write = new PrintWriter(socket.getOutputStream());  
                System.out.println("enter your message");  
                read = new BufferedReader(new InputStreamReader(System.in));  
                String smsg = read.readLine();  
                System.out.println("msg " + smsg);  
                write.println(smsg);  
                write.flush();