import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Semaphore;

public class Singleton extends Thread{

    private static volatile Singleton singleton;
    static Semaphore access=new Semaphore(1);
    static int count=0;
    static int created=0;
    private Singleton() {}

    public static Singleton getInstance() throws InterruptedException {
        // TODO: 3/29/20 Synchronize this
        access.acquire();
        count++;
        if(count==1){
            singleton = new Singleton();
            created++;
        }
        access.release();

        return singleton;
    }

    @Override
    public void run() {
        try {
            getInstance();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        // TODO: 3/29/20 Simulate the scenario when multiple threads call the method getInstance
        List<Thread> threads = new ArrayList<>();
        for(int i=0;i<100;i++){
            Singleton singleton = new Singleton();
            threads.add(singleton);
        }

        for(Thread t:threads){
            t.run();
        }

        System.out.println("Kreirana instanca: "+created);
    }

}