ForkJoin分支

ForkJoin

在jdk1.7，并行执行任务，提高效率，大数据量

把大任务拆分子任务 维护的都是双端队列

ForkJoin计算类

/**
 * 求和计算
 * ForkJoin  Stream并行流
 * 1、forkJoinPool 通过它执行
 * 2、计算任务forkJoinPool.execute(ForkJoinTask)
 * 3、计算类要继承 RecursiveTask
 */
public class ForkJoinDemo extends RecursiveTask<Long> {
    private Long start;
    private Long end;
    //临界值
    private Long temp = 10000L;
    public ForkJoinDemo(Long start, Long end) {
        this.start = start;
        this.end = end;
    }
 
    @Override
    protected Long compute() {
        if ((end - start) < temp) {
            Long sum = 0L;
            for (Long i = start; i <= end; i++) {
                sum += i;
            }
            return sum;
        } else {
            //分支合并
            Long middle = (start + end) / 2;//中间值
            ForkJoinDemo task1 = new ForkJoinDemo(start, middle);
            task1.fork();//拆分任务，把任务压入线程队列
            ForkJoinDemo task2 = new ForkJoinDemo(middle, end);
            task2.fork();//拆分任务，把任务压入线程队列
 
            return task1.join() + task2.join();
        }
 
    }
}

测试

public class Test {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //test1(); //时间：8178
        //test2();//时间：7273
        test3();//时间：207
    }
    public static void test1() {
        Long sum = 0L;
        long start = System.currentTimeMillis();
        for (Long i = 1L; i <= 10_0000_0000L; i++) {
            sum += i;
        }
        long end = System.currentTimeMillis();
        System.out.println("sum=" + sum + "时间：" + (end - start));
 
    }
    public static void test2() throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> task = new ForkJoinDemo(1L, 10_0000_0000L);
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);//提交任务
        Long sum= submit.get();
        long end = System.currentTimeMillis();
        System.out.println("sum=" + sum+" 时间：" + (end - start));
    }
    public static void test3() {
        long start = System.currentTimeMillis();
        long sum = LongStream.rangeClosed(1L, 10_0000_0000L).parallel().reduce(0, Long::sum);
        long end = System.currentTimeMillis();
        System.out.println("sum=" + sum+"时间：" + (end - start));
    }
}