Cant syncronize! Threads problem

Question

Hello everybody,
recently i posted a question(im new to threads) and it was asked immediately but now i have another
type of problem.
Please read here the initial post and the answer and please give me any ideas..
Initial Post
Hi everybody,i have this thread problem(i'm new to java and h
ave no idea what exactly to do).
Well,in my applet i have this action performed method
that i imagine is in the event dispatch thread.
This method calls as u see, two other methods of a class named CPU(.
Note that fetch and execute are observed classes and my applet class
is the observer.
The problem is that during the execution of fetch() and execute(),
inside these methods change some things and so they call notifyObservers(Object arg)
passing to the applet the argument and so the applet updates some text components.
But as you can immagine there is no time for the gui to update himself so i see nothing.
So, my question is which of the methods need to be in a separate thread so to ensure
visible results(component updating)?
Perhaps,the update method needs to be invokedLater with SwingUtilities?
Please give me an example code if possible.
Here is the actionPerformed code(from the applet class) and the fetch method:
    void executeProgramButton_actionPerformed(ActionEvent e) {      
int numInstr = this.machine.ram.segmentSize;       
for (int i = 0; i < numInstr; i = i + 4) {           
machine.cpu.fetch();           
machine.cpu.execute();       
/*The following method is in the CPU class
fetch method:here the observedPC is the observable value
that notifies the observer(the main applet)
that does: pcTextField.setText(arg.toString());*/   
public void fetchInstructionProgram() {       
observedPC = Integer.toString(pc);       
setChanged();       
notifyObservers(observedPC);       
instructions++;       
instruction=readOperation(cache.instructionfetch,pc);       
pc = pc + 4;    }
Answer to initial post
Author: stevejluke
One way could be to put the content of the action performed method into a new thread, then use invokeLater in your Observers that cause GUI updates:
    void executeProgramButton_actionPerformed(ActionEvent e) {     
new Thread()       {      
public void run()        {         
int numInstr = this.machine.ram.segmentSize;         
for (int i = 0; i < numInstr; i = i + 4)           {           
machine.cpu.fetch();           
machine.cpu.execute();         
}.start();    }
// In your Observer    public void update(Observable o, Object arg)    {     
SwingUtilities.invokeLater(new Runnable() {      
public void run()        { 
/* your GUI afecting code
});[i]
Or something like that.
You might need to watch for synchronizing things
He was right...GUI is responsive but the results...
Well,let me describe the new problem.
Here you cant see the method execute().
The problem is a synchronization problem.
Actually,what the two methods do is:fetch() updates the value of a long called instruction and execute() takes this value and do some things.Note also that the time the execute method needs to finish is not
always the same.By that, i mean that it depends on the value of the instruction updated by fetch().
By putting some System.outs before and after updating i realized that there are delays or sometimes
i noticed that fetch() executes 2 times before execute() takes control.
So,i created some synchronized private methods set and get to control access to these resources.
Better but still not correct...
What should i look?Where stays the answer?
How to synchronize these two methods on these resources?
Thank you in advance,
Chris

Answer 1

I think that your fetch and execute has a "Producer-Consumer Relationship"
in such cases you can make the producer place the produced value in to a queue and consumer take the vlues from the queue
In the producer thread it sleeps for a while and try again if the Queue is full
In the Consumer thread it sleeps for a while if the Queue is empty and then try again
Or you can do as follows
In the Producer thread it waite() if the Queue is full
In the Consumer thread it waite() if the queue is empty
When ever Producer put a value in to the Queue it calls the notify on Consumer and when ever Consumer takes a value from Queue it calls the notify() on Producer
you can even use notify all
I think thiere is no built in Queue class in java so you will have to write one here is a example
public class MyLongQueue{
            long data[];
            int head, tail;
            int size;
           public MyLongQueue(int size){
                data = new long[size];
                head = -1;
                tail = -1;
                this.size = 0;
            public synchronized boolean isFull(){
                return (size==data.length);
            public synchronized boolean isEmpty(){
                return (size==0);
            public synchronized boolean  insert(long l){
                if (size==data.length) return false; //Queue is full cant add more data
                tail = (tail + 1) % data.length;
                data[tail] = l;
                 size++;
                return true;
           public synchronized long remove(){
               if (size==0) throw new ArrayIndexOutOfBoundsException();
               size--;
               head = (head + 1) % data.length;
               return data[head];