java中fork-join的原理解析

/**
 *  累加运算测试
 */
public class ForkJoinCalculate extends RecursiveTask<Long> {
 
    /**
     * 
     */
    private static final long serialVersionUID = 7125244951292834932L;
     
    private long start;// 起始值
    private long end;// 结束值
    private static final long THRESHOLD = 10000L;// 临界值
 
    @Override
    protected Long compute() {
        long length = end - start;
         
        if(length <= THRESHOLD) {
            long sum = 0L;
             
            for (long i = start; i <= end; i++) {
                sum += i;
            }
             
            return sum;
        }else {
            long middle = (start + end) / 2;// 中间值
             
            ForkJoinCalculate left = new ForkJoinCalculate(start, middle);// 0-50000000
            left.fork();// 拆分子任务，同时压入线程队列
            ForkJoinCalculate right = new ForkJoinCalculate(middle + 1, end);// 50000001-100000000
            right.fork();// 拆分子任务，同时压入线程队列
             
            return left.join() + right.join();// 汇总任务结果
        }
    }
     
    public ForkJoinCalculate() {
    }
 
    public ForkJoinCalculate(long start, long end) {
        this.start = start;
        this.end = end;
    }
}

/**
     * Java8的顺序流
     */
    @Test
    public void test3() {
        Instant start = Instant.now();// java8中新时间日期API
         
        LongStream.rangeClosed(0, 10000000000L)
                    .sequential()// 顺序流
                    .reduce(0, Long::sum);
         
        Instant end = Instant.now();
         
        // 5780
        System.out.println("耗费时间为：" + Duration.between(start, end).toMillis());// java8中新时间日期API
    }

/**
     * Java8的并行流
     */
    @Test
    public void test4() {
        Instant start = Instant.now();// java8中新时间日期API
         
        LongStream.rangeClosed(0, 10000000000L)
                    .parallel()// 并行流
                    .reduce(0, Long::sum);
         
        Instant end = Instant.now();
         
        // 2392
        System.out.println("耗费时间为：" + Duration.between(start, end).toMillis());// java8中新时间日期API
    }