ABA问题的解决

 

代码： 

package com.dhy.mianshi.dhymianshi.aba;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.atomic.AtomicStampedReference;


public class ABADemo { //ABA问题的解决
    static AtomicReference<Integer> atomicReference = new AtomicReference<>(100);

    static AtomicStampedReference<Integer> atomicStampedReference = new AtomicStampedReference<>(100,1); // 初始值为： 100 ，版本号为： 1


    public static void main(String[] args) {
        System.out.println("=====================以下是ABA问题的产生===================================");
        new Thread(() -> {
            atomicReference.compareAndSet(100,101);
            atomicReference.compareAndSet(101,100);
        },"t1").start();

        new Thread(() -> {
            //暂停1秒钟t2线程，保证上面的t1线程完成一次ABA操作
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(atomicReference.compareAndSet(100,2019)); // 注意： 这里出现了 ABA问题
            System.out.println("atomicReference.get() : "+atomicReference.get());
        },"t2").start();

        //暂停一会线程(确保上面的线程跑完)
        try {
            TimeUnit.SECONDS.sleep(2);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("=====================以下是ABA问题的解决===================================");
        new Thread(() -> {
            int stamp = atomicStampedReference.getStamp(); // 获取版本号
            System.out.println(Thread.currentThread().getName() + "\t第1次版本号：" + stamp);
            //t3线程暂停1秒钟
            try {TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}

            atomicStampedReference.compareAndSet(100,101,atomicStampedReference.getStamp(),atomicStampedReference.getStamp()+1);
            System.out.println(Thread.currentThread().getName() + "\t第2次版本号：" + atomicStampedReference.getStamp());
            System.out.println("atomicStampedReference的值： " + atomicStampedReference.getReference());
            Boolean r = atomicStampedReference.compareAndSet(101,100,atomicStampedReference.getStamp(),atomicStampedReference.getStamp()+1);
            System.out.println("r： " + r);
            System.out.println(Thread.currentThread().getName() + "\t第3次版本号：" + atomicStampedReference.getStamp());
        },"t3").start();

        new Thread(() -> {
            int stamp = atomicStampedReference.getStamp();
            System.out.println(Thread.currentThread().getName() + "\t第1次版本号： " + stamp);
            //t4线程暂停3秒钟，能保证上面的t3线程完成一次ABA操作
            try {TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); }

            boolean result = atomicStampedReference.compareAndSet(100,2009,stamp,stamp+1);
            System.out.println("result :" + result);
            System.out.println("值 :" + atomicStampedReference.getReference());
            System.out.println("版本号 :" + atomicStampedReference.getStamp());
            },"t4").start();

    }

}

// 代码参考视频： https://haokan.baidu.com/v?pd=wisenatural&vid=5101151251744349118