Java — — AtomicStampedReference解决多线程ABA问题

package ldk.test;

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

/**
 * @Author: ldk
 * @Date: 2021/1/6 16:14
 * @Describe:
 */
public class ABA {
    private static AtomicInteger atomicInt = new AtomicInteger(100);
    private static AtomicStampedReference atomicStampedRef = new AtomicStampedReference(100, 0);

    public static void main(String[] args) throws InterruptedException {
        Thread intT1 = new Thread(new Runnable() {
            @Override
            public void run() {
                atomicInt.compareAndSet(100, 101);
                atomicInt.compareAndSet(101, 100);
            }
        });

        Thread intT2 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                }
                boolean c3 = atomicInt.compareAndSet(100, 101);
                System.out.println(c3); // true
            }
        });

        intT1.start();
        intT2.start();
        intT1.join();
        intT2.join();

        Thread refT1 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                }
                System.out.println("1-1:"+atomicStampedRef.getStamp());
                atomicStampedRef.compareAndSet(100, 101, atomicStampedRef.getStamp(), atomicStampedRef.getStamp() + 1);
                System.out.println("1-2:"+atomicStampedRef.getStamp());
                atomicStampedRef.compareAndSet(101, 100, atomicStampedRef.getStamp(), atomicStampedRef.getStamp() + 1);
                System.out.println("1-3:"+atomicStampedRef.getStamp());
            }
        });

        Thread refT2 = new Thread(new Runnable() {
            @Override
            public void run() {
                int stamp = atomicStampedRef.getStamp();
                try {
                    TimeUnit.SECONDS.sleep(2);
                } catch (InterruptedException e) {
                }
                System.out.println("2-1:"+atomicStampedRef.getStamp());
                boolean c3 = atomicStampedRef.compareAndSet(100, 101, stamp, stamp + 1);
                System.out.println("2-2:"+atomicStampedRef.getStamp());

                System.out.println(c3); // false
            }
        });

        refT1.start();
        refT2.start();
    }
}

未使用AtomicStampedReference之前，没有版本的概念，值再怎么变化，操作是可以成功的。

使用AtomicStampedReference时候，有了版本的概念，版本一旦发生变化，操作就会失败。