并发学习--Future机制核心_future 的机制-优快云博客

本文链接：https://blog.youkuaiyun.com/ARSLYN/article/details/113334487

本文通过示例展示了如何基于Java并发库实现一个自定义的`FutureTask`，利用`Callable`和`ExecutorService`进行异步计算，并在主线程中阻塞等待结果。同时，参考了`FutureTask`的源码，了解其核心思想。

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package com.example.demo.AQS;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * @program: demo
 * @description: future
 * @author: 郭雄帅
 * @create: 2021-01-27 09:56
 */
public class FutureDemo {

    static ExecutorService  executors= Executors.newScheduledThreadPool(2);
    public static void main(String[] args) {
        Callable<String> callable = new Callable<String>() {
            @Override
            public String call() throws Exception {
                return "lalala";
            }
        };

        JackFuture<String> futureTask = new JackFuture<>(callable);
        new Thread(futureTask).start();
        System.out.println(futureTask.getResult());
    }
}

下面的代码参考java.util.concurrent.FutureTask源码

package com.example.demo.AQS;

import java.util.concurrent.Callable;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.locks.LockSupport;

/**
 * @program: demo
 * @description:FutureTask的核心思想
 * @author: 郭雄帅
 * @create: 2021-01-27 09:57
 */
public class JackFuture<T> implements Runnable{
    private Callable<T> callable;
    T result;
    volatile String status = "NEW";
    LinkedBlockingQueue<Thread> queue = new LinkedBlockingQueue<>();
    public JackFuture(Callable<T> callable) {
        this.callable = callable;
    }

    public T getResult() {//阻塞，run方法执行完毕之后
        System.out.println("执行get");
        if ("END".equals(status)){

            return result;
        }
        while (!"END".equals(status)){//run未完成，执行阻塞
            //准备一个容器，存放线程
            queue.offer(Thread.currentThread());
            LockSupport.park();
        }

        return result;
    }

    @Override
    public void run() {
        try {
            System.out.println(Thread.currentThread().getName()+"+执行run");
            result = callable.call();
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            status="END";
        }
        Thread thread = queue.poll();
        while (thread!=null){
            LockSupport.unpark(thread);
            thread = queue.poll();//直到全部取出，结束循环
        }
    }
}

```又学到了！