Exercise 2

import java.util.concurrent.Semaphore;

public class ConcurrentThreadsSemaphore {
	public static Semaphore semaphore = new Semaphore(1);
    public static int value;
    public static final int ITERATIONS = 1000000;

    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new IncrementProblemThread(0, ITERATIONS);
        Thread t2 = new IncrementProblemThread(1, ITERATIONS);

        t1.start();
        t2.start();

        t1.join();
        t2.join();

        System.out.println("final value = " + value);
    }
}

class IncrementProblemThread extends Thread {
    int id;
    private int iterations;
    private long start;
    private long end;

    public IncrementProblemThread(int id, int iterations) {
        this.id = id;
        this.iterations = iterations;
    }

    public void run() {
        try {
            start = System.currentTimeMillis();

            for (int i = 0 ; i < iterations ; ++i) {
				ConcurrentThreadsSemaphore.semaphore.acquire();
                ConcurrentThreadsSemaphore.value++;
                ConcurrentThreadsSemaphore.semaphore.release();
            }

            end = System.currentTimeMillis();    
        } catch (Exception e) {
            System.out.println("Exception: " + e);
        }

        System.out.println("ID: " + id + ", Runtime [ms]: " + (end - start));
    }
}

javac ConcurrentThreadsSemaphore.java

java ConcurrentThreadsSemaphore
ID: 1, Runtime [ms]: 137
ID: 0, Runtime [ms]: 133
final value = 2000000

java ConcurrentThreadsSemaphore
ID: 0, Runtime [ms]: 120
ID: 1, Runtime [ms]: 108
final value = 2000000

java ConcurrentThreadsSemaphore
ID: 0, Runtime [ms]: 128
ID: 1, Runtime [ms]: 128
final value = 2000000