import java.util.concurrent.*;

class Test implements Runnable {

    static int numberOfThreads;
    static CyclicBarrier barrier;

    public static void main(String[] args) throws InterruptedException {

        // TEST WITH 4 THREADS

        numberOfThreads = 4;
        barrier = new CyclicBarrier(numberOfThreads);

        long start = System.currentTimeMillis();
        Test t = new Test();
        Thread[] threads = new Thread[numberOfThreads];
        for (int i = 0; i < numberOfThreads; i++)
            (threads[i] = new Thread(t)).start();

        for (Thread thread : threads)
            thread.join();

        System.out.println("4 threads: " + (System.currentTimeMillis() - start));



        // TEST WITH 1 THREAD
        numberOfThreads = 1;
        barrier = new CyclicBarrier(numberOfThreads);

        start = System.currentTimeMillis();
        t = new Test();
        threads = new Thread[numberOfThreads];
        for (int i = 0; i < numberOfThreads; i++)
            (threads[i] = new Thread(t)).start();

        for (Thread thread : threads)
            thread.join();

        System.out.println("1 thread: " + (System.currentTimeMillis() - start));

    }





    public void run() {

        int i = 0;

        while (i++ < 5) {
            try {

                // perform an ammount of computations inversely proportional to
                // the number of threads.
                for (int j = 0; j < 10000 / numberOfThreads; j++)
                    countPrimes();

                barrier.await(); // CyclicBarrier waiting for all threads
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }


    public void countPrimes() {

        int i = 0;
        int primeNumberCounter = 0;

        while (++i <= 1000) {

            int i1 = (int) Math.ceil(Math.sqrt(i));

            boolean isPrimeNumber = false;

            while (i1 > 1) {

                if ((i != i1) && (i % i1 == 0)) {
                    isPrimeNumber = false;
                    break;
                } else if (!isPrimeNumber) {
                    isPrimeNumber = true;
                }

                --i1;
            }

            if (isPrimeNumber)
                ++primeNumberCounter;
        }
    }

}