/* PrimeCounterBetterLoad.java
 * Use Java threading to count the number of prime
 * numbers between 0 and a large number N
 * 
 * The load balancing is not great in this version
 *
 * javac PrimeCounterBetterLoad.java
 * java PrimeCounterBetterLoad
 */
public class PrimeCounterBetterLoad implements Runnable {
	private int id;
	private int N;
	private int chunk_size;
	private int num_threads;
	private int count;
	
	public PrimeCounterBetterLoad (int id, int N,  int chunk_size, int num_threads) {
		this.id = id;
		this.N = N;
		this.chunk_size = chunk_size;
		this.num_threads = num_threads;
		this.count = 0;
	}
	
	public boolean is_prime (int n) {
		if (n < 2) return false;
		if (n == 2) return true;
		if (n%2 == 0) return false;
		for (int i = 3; i < n; i += 2) {
            if (n % i == 0) return false;
		}
		return true;
	}
	
	public void run () {
        int start = this.chunk_size * this.id;
        for (int i = start; i < N; i = i + chunk_size*num_threads ) {
            for (int j = 0; j < chunk_size; j++) {
                if (is_prime(i+j))
    				count += 1;
			}
		}
	}
	
	public int count () {
		return count;
	}
	
	public static void main (String args[]) {
		int N = 1000000;
		
        int chunk_size = 100;
        int NUM_THREADS = 8;
        
        PrimeCounterBetterLoad pc[] = new PrimeCounterBetterLoad[NUM_THREADS];
        Thread threads[] = new Thread[NUM_THREADS];
        
        for (int i = 0; i < NUM_THREADS; i++ ) {
            pc[i] = new PrimeCounterBetterLoad(i, N, chunk_size, NUM_THREADS);
            threads[i] = new Thread(pc[i]);
        }
        
		PrimeCounterBetterLoad pc0 = new PrimeCounterBetterLoad(0, N, N, 1);
		Thread t0 = new Thread(pc0);
		
		long start = System.currentTimeMillis();
		
		for (int i = 0; i < NUM_THREADS; i++)   threads[i].start();
		try {
		    for (int i = 0; i < NUM_THREADS; i++)   threads[i].join();
		} catch (Exception e) {
			System.err.println(e);
		}
		
		int count = 0;
        for (int i = 0; i < NUM_THREADS; i++)   count += pc[i].count();
		
		long end = System.currentTimeMillis();
		System.out.printf("Multi-threads count %d primes in %d ms\n", count, end-start);
		
		// Time sequential solution, but using 1 thread
		start = System.currentTimeMillis();
		
		t0.start();
		try {
			t0.join();
		} catch (Exception e) {
			System.err.println(e);
		}
		
		count = pc0.count();
		
		end = System.currentTimeMillis();
		System.out.printf("One threads count %d primes in %d ms\n", count, end-start);
	}
}