ForkJoin sample

ForkJoinArrayEvaluator.java

package mireyn;

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveAction;

public class ForkJoinArrayEvaluator {
    private static final int CPU = Runtime.getRuntime().availableProcessors();
    public static int THRESHOLD = CPU * 16;

    public int[] evaluate(int[] data, int p) throws InterruptedException {
        if (data == null) {
            throw new IllegalArgumentException("Data must not be null");
        }
        if (data.length == 0) {
            return data;
        }
        final ForkJoinPool pool = new ForkJoinPool();
        pool.invoke(new EvalTask(data, 0, data.length, p));
        return data;
    }

    private static class EvalTask extends RecursiveAction {
        EvalTask(int[] data, int start, int stop, int p) {
            this.data = data;
            this.start = start;
            this.stop = stop;
            this.p = p;
        }

        @Override
        protected void compute() {
            if ((stop - start) <= THRESHOLD) {
                for (int i = start; i < stop; i++) {
                    data[i] = (int) Math.pow(data[i], p); // ExtLib.eval(data[i], p);
                }
            } else {
                final int mid = (start + stop) >>> 1;
                ForkJoinTask.invokeAll(
                        new EvalTask(data, start, mid, p),
                        new EvalTask(data, mid, stop, p)
                );
            }
        }

        private final int[] data;
        private final int start;
        private final int stop;
        private final int p;
    }
}