JUC(13) - ForkJoinPool 分支/合并框架 工

13. ForkJoinPool 分支/合并框架 工作窃取

Fork/Join 框架：就是在必要的情况下，将一个大任务，进行拆分(fork)成若干个小任务（拆到不可再拆时），再将一个个的小任务运算的结果进行 join 汇总

class ForkJoinSumCalculate extends RecursiveTask<Long> {

    private static final long serialVersionUID = -259195479995561737L;

    private long start;

    private long end;

    /**
     * 临界值
     */
    private static final long THRESHOLD = 10000L;

    public ForkJoinSumCalculate(long start, long end) {
        this.start = start;
        this.end = end;
    }

    @Override
    protected Long compute() {
        long len = end - start;
        if (len <= THRESHOLD) {
            long sum = 0;

            for (long i = start; i <= end; i++) {
                sum += i;
            }
            return sum;
        } else {
            long middle = (start + end) / 2;
            ForkJoinSumCalculate left = new ForkJoinSumCalculate(start, middle);
            //进行拆分, 同时压入线程队列
            left.fork();

            ForkJoinSumCalculate right = new ForkJoinSumCalculate(middle, end);
            //进行拆分, 同时压入线程队列
            right.fork();

            return left.join() + right.join();

        }
    }
}

测试

    public static void main(String[] args) {
        Instant start = Instant.now();

        ForkJoinPool pool = new ForkJoinPool();

        ForkJoinSumCalculate task = new ForkJoinSumCalculate(0L, 50000000000L);

        Long sum = pool.invoke(task);

        System.out.println(sum);

        Instant end = Instant.now();
        System.out.println("耗费时间为：" + Duration.between(start, end).toMillis());
    }