Networking and Multithreading

[Daniel Simpson]

Hi, I am beginning to make an outline of my networking approach. I have a question about threads. When a new client in networked mode launches the application and a new thread is spawned, what should be in the run method? Thanks!
[ December 13, 2004: Message edited by: Daniel Simpson ]

[Andrew Monkhouse]

Hi Daniel,

I am not sure that I understand your question, so if I am going off on a tangent, please ignore my ramblings and if you can spot where I have misunderstood you then please correct me.

If you are talking about using the SwingUtilities.invokeLater() to explicitly start a new thread to do the booking, then you probably want your runnable method to contain all the method calls needed to do a booking. You might want some to use some sort of Observable pattern to get information back to the main thread about success / failure of the booking process.

If you are talking about using Sockets to connect to the server, then there are plenty of tutorials showing how to do this. The simplest way to do this is to spawn a new thread as soon as you have a connection, then the runnable method will open your streams and start sending and receiving data on them.

We should not be talking about RMI, since RMI creates it's own threads.

Regards, Andrew

[Daniel Simpson]

Thanks for your reply, Andrew. In my implementation of the book method, it goes, lock-->verify data-->update(book)-->unlock. I guess my question is, if I call the book method from the run method, how do I pass the parameter of the record number into the run method?

[Andrew Monkhouse]

Hi Daniel,

I still don't know which run method you are talking about, although I am still leaning towards you talking about using the SwingUtilities.runLater() method.

Take a look at the following code:

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
 
public class GraphicDemo extends JFrame implements ActionListener, Observer {
    public JButton clickableButton = new JButton("Click me");
 
    public static void main(String[] args) {
        new GraphicDemo();
    }
 
    public GraphicDemo() {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        clickableButton.addActionListener(this);
        getContentPane().add(clickableButton);
        pack();
        show();
    }
 
    public void actionPerformed(ActionEvent e) {
        clickableButton.setEnabled(false);
        SwingUtilities.invokeLater(new MakeBooking(this, "button clicked"));
    }
 
    public void update(Observable o, Object arg) {
        if (arg instanceof Exception) {
            System.out.println("Something failed somewhere");
        }
        clickableButton.setEnabled(true);
    }
}
 
class MakeBooking extends Observable implements Runnable {
    private Object someValue;
    Random random = new Random();
 
    public MakeBooking(Observer creator, Object someValue) {
        addObserver(creator);
        this.someValue = someValue;
    }
 
    public void run() {
        long timeToWait = random.nextInt(5) + 5;
        System.out.println("Doing something with " + someValue);
        System.out.println("This will take " + timeToWait + " seconds to run");
        try {
            Thread.sleep(timeToWait * 1000);
        } catch (InterruptedException ignored) {
            // don't swallow exceptions like this in your real assignment !
        }
        setChanged();
        notifyObservers("Did something");
        System.out.println("all done - button should be enabled again");
    }
}

Does this provide you with an answer?

As you can see, I am passing parameters into, and out of, the separate thread that I am creating in order to do the real work.

Regards, Andrew

[Daniel Simpson]

I'm fairly new to networking/multithreading so I am sorry for all the confusion. Forgive me if I am wrong, but in the code, wouldn't there need to be a thread creation using Runnable parameter from your inner class and also calling the start() method on that thread?? Also, the run method I was referring to was

public void run()

. Thanks!

[Omar Kalaldeh]

Hi Daniel,
From what I have read, I don’t think you are handling client requests within thread pool, if not I think you should consider it, it is not a necessity but handling requests in a thread pool is always better.

Any way, as for how to handle requests at server side, you can set accepted socket client in the constructor of your handling thread (that is if you are not using thread pool).

Your code in very simple way could look like:

        while (true) {
        socket = serverSocket.accept();
               HandlerThread handler = new HandlerThread(socket);
               t.start();  
        }

Now inside your run method you will read request Object and handle it there.

[Daniel Simpson]

That makes sense! Thanks Omar!