ForkJoinDemo

public class ForkJoinPoolTest {

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        int[] arr = new int[]{1,2,3,4,5,6};

        LongSum longSum = new LongSum(0,arr.length,arr);

        ExecutorService executorService = Executors.newCachedThreadPool();

//        executorService.submit(longSum);

        ForkJoinPool forkJoinPool = new ForkJoinPool(12);
        ForkJoinTask<Long> submit = forkJoinPool.submit(longSum);
        Long aLong = submit.get();
        System.out.println(aLong);

        forkJoinPool.shutdown();

    }

   static class LongSum extends RecursiveTask<Long> {

        static final int SEQUENTIAL_THREAD = 1000;

        int low;
        int high;

        int[] arr;

        LongSum(int low,int high,int[] arr){
            this.low = low;
            this.high = high;
            this.arr = arr;

        }
        @Override
        protected Long compute() {
            if(high-low<=SEQUENTIAL_THREAD){
                long sum = 0;
                for(int i = low; i<high;i++){
                    sum+=arr[i];
                }
                return sum;
            }else {
                int mid = low+(high-low)/2;
                LongSum left = new LongSum(low, mid, arr);
                LongSum right = new LongSum(mid, high, arr);
                left.fork();
                right.fork();

                Long r = right.join();
                Long l = left.join();
                return r+l;
            }
        }
    }
}