import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.*;

/**
 * Class to use parallelism to compute the sum of two vectors. Extends
 * RecursiveAction, which itself extends ForkJoinTask<Void>
 * 
 * @author kim
 * @version 2/20/2011
 */
public class VecAdd extends RecursiveAction {
	private static final int VECTOR_SIZE = 200;

	private static final ForkJoinPool fjPool = new ForkJoinPool();

	private static final int SEQUENTIAL_CUTOFF = 50;
	int lo;
	int hi;
	int[] res;
	int[] arr1;
	int[] arr2;

	public VecAdd(int l, int h, int[] r, int[] a1, int[] a2) {
		lo = l;
		hi = h;
		res = r;
		arr1 = a1;
		arr2 = a2;
	}

	protected void compute() {
		if ((hi - lo) < SEQUENTIAL_CUTOFF) {
			for (int i = lo; i < hi; i++) {
				res[i] = arr1[i] + arr2[i];
			}
		} else {
			int mid = (hi + lo) / 2;
			VecAdd left = new VecAdd(lo, mid, res, arr1, arr2);
			VecAdd right = new VecAdd(mid, hi, res, arr1, arr2);
			left.fork();
			right.compute();
			left.join();
		}
	}

	public static int[] add(int[] arr1, int[] arr2) {
		assert (arr1.length == arr2.length);
		int[] ans = new int[arr1.length];
		fjPool.invoke(new VecAdd(0, arr1.length, ans, arr1, arr2));
		return ans;
	}
	
	public static void main(String[] args) {
		int[] first = new int[VECTOR_SIZE];
		int[] second = new int[VECTOR_SIZE];
		for(int count = 0; count < VECTOR_SIZE; count++) {
			first[count] = count;
			second[count] = 2*count;
		}
		int[] answer = add(first,second);
		for(int val:answer) {
			System.out.print(val+", ");
		}
	}
}