public class Example {
    private int state = 0;
    public void doSomething() {
        if (state == 0) {
            state = 1;
        }
    }
}

public class Example {
    
    private volatile int state = 0;
    private static final Unsafe UNSAFE = Unsafe.getUnsafe();
    private static final long stateOffset;

    static {
        try {
            stateOffset = UNSAFE.objectFieldOffset(Example.class.getDeclaredField("state"));
        } catch (Exception ex){
            throw new Error(ex);
        }
    }

    public void doSomething() {
        if (UNSAFE.compareAndSwapInt(this, stateOffset, 0 ,1)) {
            // TODO
        }
    }

    public int getState() {
        return state;
    }
}

public static void main(String[] args) {
    Example example = new Example();
    example.doSomething();
    System.out.println(example.getState());
}

@CallerSensitive
public static Unsafe getUnsafe() {
    Class var0 = Reflection.getCallerClass();
    if (!VM.isSystemDomainLoader(var0.getClassLoader())) {
        throw new SecurityException("Unsafe");
    } else {
        return theUnsafe;
    }
}

public static void main(String[] args) {

    Book javaBook = new Book(1,"javaBook");

    // 參數(shù)1是版本號(hào)
    AtomicStampedReference<Book> stampedReference = new AtomicStampedReference<>(javaBook,1);

    System.out.println(stampedReference.getReference() + "\t" + stampedReference.getStamp());

    Book mysqlBook = new Book(2,"mysqlBook");

    boolean b;
    // 在判斷的時(shí)候不斷要判斷book,還要判斷版本號(hào),更新的時(shí)候更新book的值,也要更新版本號(hào)(這里是加1)
    b = stampedReference.compareAndSet(javaBook, mysqlBook, stampedReference.getStamp(), stampedReference.getStamp() + 1);

    System.out.println(b + "\t" + stampedReference.getReference() + "\t" + stampedReference.getStamp());

    b = stampedReference.compareAndSet(mysqlBook, javaBook, stampedReference.getStamp(), stampedReference.getStamp() + 1);

    System.out.println(b+"\t"+stampedReference.getReference()+"\t"+stampedReference.getStamp());

}

public class ABADemo {
    static AtomicStampedReference<Integer> stampedReference = new AtomicStampedReference<>(100,1);
    public static void main(String[] args) {
        new Thread(() -> {
            int stamp = stampedReference.getStamp();
            System.out.println(Thread.currentThread().getName() + "\t" + "首次版本號(hào)：" + stamp);
            // 暫停500毫秒,保證后面的t4線程初始化拿到的版本號(hào)和我一樣
            try { TimeUnit.MILLISECONDS.sleep(500); } catch (InterruptedException e) { e.printStackTrace(); }
            // 從100改到101
            stampedReference.compareAndSet(100,101,stampedReference.getStamp(),stampedReference.getStamp()+1);
            System.out.println(Thread.currentThread().getName()+"\t"+"2次流水號(hào)："+stampedReference.getStamp());
            // 從101改到100
            stampedReference.compareAndSet(101,100,stampedReference.getStamp(),stampedReference.getStamp()+1);
            System.out.println(Thread.currentThread().getName()+"\t"+"3次流水號(hào)："+stampedReference.getStamp());
        },"t3").start();
        new Thread(() -> {
            int stamp = stampedReference.getStamp();
            System.out.println(Thread.currentThread().getName()+ "\t" + "首次版本號(hào)：" + stamp);
            // 暫停1秒鐘線程,等待上面的t3線程，發(fā)生了ABA問(wèn)題
            try { TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { e.printStackTrace(); }
            boolean b = stampedReference.compareAndSet(100, 2022, stamp, stamp + 1);
            System.out.println(b+"\t"+stampedReference.getReference()+"\t"+stampedReference.getStamp());
        },"t4").start();
    }
}