第三章-原子类AtomicInteger-ABA问题

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是什么

image-20191107103120391

案例

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static AtomicReference<Integer> atomicReference = new AtomicReference<>(100);
private static void atomicReferenceABA() {
    new Thread(() -> {
        atomicReference.compareAndSet(100, 101);
        atomicReference.compareAndSet(101, 100);
    }, "t1").start();
    new Thread(() -> {
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(atomicReference.compareAndSet(100, 2019) + "\t" + atomicReference.get());
    }, "t2").start();
}

public static void main(String[] args) {
    // 基础版
    atomicReferenceABA();
}

如何解决

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public static void main(String[] args) {
    // 改良版
    atomicStampedReferenceABA();
}

static AtomicStampedReference<Integer> atomicReference2 = new AtomicStampedReference<>(100, 1);
private static void atomicStampedReferenceABA() {
    new Thread(() -> {
        atomicReference2.compareAndSet(100, 101, 1, atomicReference2.getStamp()+1);
        atomicReference2.compareAndSet(101, 100, 2, atomicReference2.getStamp()+1);
    }, "t1").start();
    new Thread(() -> {
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(atomicReference2.compareAndSet(100, 2019, 1, atomicReference2.getStamp()+1) + "\t" + atomicReference.get() + "\t" + atomicReference2.getStamp());
    }, "t2").start();
}