Java中Fork/Join示例

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

public class SumTask extends RecursiveTask<Long> {

    static final int THRESHOLD = 100;
    long[] array;
    int start;
    int end;

    SumTask(long[] array, int start, int end) {
        this.array = array;
        this.start = start;
        this.end = end;
    }

    @Override
    protected Long compute() {
        if (end - start <= THRESHOLD) {
            long sum = 0;
            for (int i = start; i < end; i++) {
                sum += array[i];
            }
            System.out.println(String.format("compute %d~%d = %d", start, end, sum));
            return sum;
        }

        int middle = (start + end) / 2;
        System.out.println(String.format("split%d~%d ==> %d~%d, %d~%d", start, end, start, middle, middle, end));
        SumTask subTask1 = new SumTask(this.array, start, middle);
        SumTask subTask2 = new SumTask(this.array, middle, end);

        invokeAll(subTask1, subTask2);
        Long subResult1 = subTask1.join();
        Long subResult2 = subTask2.join();

        long result = subResult1 + subResult2;
        System.out.println("result = " + subResult1 + " + " + subResult2 + " ==> " + result);
        return result;
    }

    public static void main(String[] args) {
        long[] array = new long[800];
        for (int i = 0; i < array.length; i++) {
            array[i] = i + 1;
        }

        // fork/join task
        ForkJoinPool fjp = new ForkJoinPool(4);
        ForkJoinTask<Long> task = new SumTask(array, 0, array.length);
        long startTime = System.currentTimeMillis();
        long result = fjp.invoke(task);
        long endTime = System.currentTimeMillis();
        System.out.println("Fork/Join sum: " + result + " in: " + (endTime - startTime) + " ms");
    }
}

程序執行結果