Java Multithreading - Threadsafe Counter

Question

I\'m starting off with a very simple example in multithreading. I\'m trying to make a threadsafe counter. I want to create two threads that increment the counter intermitten

Answer 1

Well, with your code I don't know how to get "exactly" intermittently, but if you use Thread.yield() after call incrementCounter() you will have a better distribution.

public void run() {
         while(counter<1000){
              incrementCounter();
              Thread.yield();

         }
    }

Otherwise, to get what you propose, you can create two different thread class (ThreadsExample1 and ThreadsExample2 if you want), and another class to be a shared variable.

public class SharedVariable {
    private int value;
    private boolean turn; //false = ThreadsExample1 --> true = ThreadsExample2

    public SharedVariable (){
        this.value = 0;
        this.turn = false;
    }

    public void set (int v){
        this.value = v;
    }

    public int get (){
        return this.value;
    }

    public void inc (){
        this.value++;
    }

    public void shiftTurn(){
        if (this.turn){
            this.turn=false;
        }else{
            this.turn=true;
        }
    }

    public boolean getTurn(){
        return this.turn;
    }

}

Now, the main can be:

public static void main(String[] args) {
        SharedVariable vCom = new SharedVariable();
        ThreadsExample1 hThread1 = new ThreadsExample1 (vCom);
        ThreadsExample2 hThread2 = new ThreadsExample2 (vCom);

        hThread1.start();
        hThread2.start();

        try {
            hThread1.join();
            hThread2.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }

And you have to change your line static int counter = 1; // a global counter for private SharedVariable counter;

And the new run is:

public void run() {
    for (int i = 0; i < 20; i++) {
        while (!counter.getTurno()){
            Thread.yield();
        }
        System.out.println(this.counter.get());
        this.counter.cambioTurno();
    }
}

}

Yes, it is another code, but I think it can help you a little bit.