同步两个彼此不认识的线程[Java]

Question

First of all, excuse my poor english =S Second, sorry if my title is a little weird, I didn't know how to formulate it better.

I have a little problem. I'm developing a game in Java and I'm using the MVC pattern the way it has been taught to me. I don't know if this is the most efficient way but anyway, here is the overall thing : 4 packages : model, view, controler, and "observer".

In observer, there is one interface "Observer", in which are defined all the methods that an element "observing the model" should implement. There is also a class "Observable", with a list of observers, and all the methods notifying them of some changes (methods like "fireEvent1(int i) { for (Observer obs: observers) obs.Event1(i); }") The model extends the class Observable and some elements of the GUI implements the interface Observer.

Now my problem is : In a method in the model, I want the model to "wait" for 2 user interactions. That means something like that :

• method called in the model
• do some stuff
• wait for the user to interact the 1st time
• get informations about what the user just did (which are collected in the controler)
• do some stuff
• wait for the user to interact the 2nd time
• get informations
• do stuff
• end

One precision : the interactions of the user are collected in the controler which implements ActionListener, and the elements of the view have the controler as ActionListener.

So I suppose I have to use threads, but despite all the tutorials and exemples I have found, I'm still not able to make this work. I tried to start a thread in the model, make it wait, but I just can't achieve making another thread in the controler, synchronized with the first one and notify it when necessary. I don't even know if this is the right thing to do, anyway, I've been on this problem for hours and I just don't know how to solve it.

I hope my explanations were clear, if not, please feel free to ask, I will then try to write a simple code representing my problem.

Thanks for your help

Scentle5S

EDIT: Here is a small code representing my problem. So I would like the model to be able to get the informations from the view, one after the another, only two times. I start a thread in the model and make it wait (by the way, I saw many times that infinite loop to make the thread wait, but I don't understand why it is necessary. Wouldn't a simple call to wait(), with no loop, do the job as well ?).

But it is obvious that there is no other thread here synchronized with the model, which would be able able to notify when the action is performed and transmit the data.

I have no idea how to do such a thing.

public class Model extends Observable {

    public void waitForActions() {
        System.out.println("Wating for two user's actions");

        Thread t = new Thread() {
            public void run() {
                while (true) {
                    try {
                        wait();
                    } catch (InterruptedException e) {
                    }
                }
                System.out.println("First action received in model : "
                        + message);
                while (true) {
                    try {
                        wait();
                    } catch (InterruptedException e) {
                    }
                }
                System.out.println("Second action received in model : "
                        + message);
            }
        };
        fireWaitForActions(true);
        t.start();
        fireWaitForActions(false);
    }
}

public class Controler implements ActionListener {
    private Model model;

    public Controler(Model model) {
        this.model = model;
    }

    public void actionPerformed(ActionEvent e) {
        String message = ((JButton)e.getSource()).getText();
        System.out.println("Action received in controler : "+message);
    }
}

public class View extends JFrame implements Observer {
    private JButton b1 = new JButton("Action 1");
    private JButton b2 = new JButton("Action 2");
    private Controler controler;

    public View(Controler controler) {
        this.controler = controler;

        b1.addActionListener(controler);
        b2.addActionListener(controler);

        b1.setEnabled(false);
        b2.setEnabled(false);

        JPanel container = new JPanel();
        container.add(b1);
        container.add(b2);
        setContentPane(container);
        pack();
        setLocationRelativeTo(null);
        setVisible(true);
    }

    public void waitForActions(Boolean b) {
        b1.setEnabled(b);
        b2.setEnabled(b);       
    }
}

public static void main(String[] args) {
    Model model = new Model();
    Controler controler = new Controler(model);
    View view = new View(controler);
    model.addObserver(view);
    model.waitForActions();
}

Here are the Observable and Observer classe/interface :

public class Observable {
    private LinkedList<Observer> observers = new LinkedList<Observer>();

    public void addObserver(Observer obs) {
        observers.add(obs);
    }

    public void fireWaitForActions(boolean b) {
        for (Observer obs: observers) obs.waitForActions(b);
    }
}

public interface Observer {
    public void waitForActions(Boolean b);
}

Answer 1

There are a number of ways to do this. Look in your Java language manual for thread synchronization methods.

You can use wait() and notify() on an Object that both threads can see. You can use acquire() and release() on a Semaphore that both threads can see. You can probably build a solution using Blocking Queues.

wait()/notify() or acquire()/release() are probably easiest.

Answer 2

To synchronize two (or more threads) not being able to know each other you need an object common to both of the Threads. You can easily use a lock from the

java.util.concurrent.locks

package.

http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/locks/package-summary.html

For example create a ReentranceLock and simply use

.lock()

and

.unlock()

Answer 3

I think its a little confusing explanation given by you or you misunderstood your own requirement. Whenever there is a request coming to your web container its will create a thread for handling thi srequest. Are you talking about those threads or can you explain what is the requirement yu want to met in detai.