Java中ForkJoin的临界值怎么选择比较好？

渊蓝 2021-07-22 22:16:33

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

public class ForkJoinTest {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        test1();
        System.out.println();
        test2();
    }

    /**
     * 直接单线程执行，作为对比
     */
    public static void test1(){
        Long sum = 0L;
        Long start = System.currentTimeMillis();
        for (Long i = 1L; i <=10000000000L; i++) {
            sum = sum + i;
        }
        Long end = System.currentTimeMillis();
        System.out.printf("结果为：%d，耗时：%d",sum,(end-start));
    }
    /**
     * 使用ForkJoin
     */
    public static void test2() throws ExecutionException, InterruptedException {
        Long start = System.currentTimeMillis();
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinDemo forkJoinDemo = new ForkJoinDemo(1L,10000000000L);
        ForkJoinTask<Long> forkJoinTask = forkJoinPool.submit(forkJoinDemo);
        Long sum = forkJoinTask.get();
        Long end = System.currentTimeMillis();
        System.out.printf("结果为：%d，耗时：%d",sum,(end-start));
    }

   
}


class ForkJoinDemo extends RecursiveTask<Long>{
    //临界值设置
    private static final long THRESHOLD = 25000000L;
    private Long start;
    private Long end;

    public ForkJoinDemo(Long start, Long end) {
        this.start = start;
        this.end = end;
    }

    @Override
    protected Long compute() {
        if (end-start<=THRESHOLD){
            Long sum = 0L;
            for (Long i = start; i <= end; i++) {
                sum+=i;
            }
            return sum;
        }else{
            //ForkJoin
            Long middle = (start + end)/2;
            //拆分线程
            ForkJoinDemo task1 = new ForkJoinDemo(start,middle);
            //把线程压入队列
            task1.fork();
            ForkJoinDemo task2 = new ForkJoinDemo(middle+1,end);
            task2.fork();
            return task1.join()+task2.join();
        }
    }
}

...全文