java | Fork/Join

Fork/Join 体现了分而治之的思想，适用于能够进行任务拆分的 CPU 密集型计算。

所谓的任务拆分，是将一个大任务拆分为算法上相同的小任务，直至不能拆分可以直接求解。

Fork/Join 在分治的基础上加入了多线程，可以把每个人物的分解和合并交给不同的线程来完成，进一步提升了运行效率。

Fork/Join 默认会创建与 CPU 核心数大小相同的线程池。

package com.redisc;

import lombok.extern.slf4j.Slf4j;

import java.time.DayOfWeek;
import java.time.Duration;
import java.time.LocalDateTime;
import java.util.concurrent.*;

@Slf4j(topic = "c.Test")
public class Run {

public static void main(String[] args) throws InterruptedException, ExecutionException {
        ForkJoinPool pool = new ForkJoinPool(4);
        System.out.println(pool.invoke(new MyTask(5)));
    }
}

@Slf4j(topic = "c.MyTask")
class MyTask extends RecursiveTask<Integer> {
    private int n;

public MyTask(int n) {
        this.n = n;
    }

@Override
    public String toString() {
        return "{" + n + "}";
    }

@Override
    protected Integer compute() {
        // 终止条件
        if (n == 1) {
            log.debug("join() {}", n);
            return 1;
        }
        MyTask t1 = new MyTask(n - 1);
        t1.fork(); // 让一个线程去执行任务
        log.debug("fork() {} + {}", n, t1);
        int result = n + t1.join(); //获取任务结果
        log.debug("join() {} + {} = {}", n, t1, result);
        return result;
    }
}

13:26:54.812 [ForkJoinPool-1-worker-1] DEBUG c.MyTask - fork() 5 + {4}
13:26:54.812 [ForkJoinPool-1-worker-2] DEBUG c.MyTask - fork() 4 + {3}
13:26:54.812 [ForkJoinPool-1-worker-0] DEBUG c.MyTask - fork() 2 + {1}
13:26:54.812 [ForkJoinPool-1-worker-3] DEBUG c.MyTask - fork() 3 + {2}
13:26:54.815 [ForkJoinPool-1-worker-0] DEBUG c.MyTask - join() 1
13:26:54.816 [ForkJoinPool-1-worker-0] DEBUG c.MyTask - join() 2 + {1} = 3
13:26:54.816 [ForkJoinPool-1-worker-3] DEBUG c.MyTask - join() 3 + {2} = 6
13:26:54.816 [ForkJoinPool-1-worker-2] DEBUG c.MyTask - join() 4 + {3} = 10
13:26:54.816 [ForkJoinPool-1-worker-1] DEBUG c.MyTask - join() 5 + {4} = 15
15

使用场景过少，不多说了。