JUC之volatile

/**
 * @desc volatile可见性、非原子性验证
 * @Date 2019/8/19
 */
public class VolatileDemo {
    public static void main(String[] args) {
        // 验证可见性
        seeOkVisibility();
        // 验证非原子性
        seeNonAtomic();
    }

    private static void seeNonAtomic() {
        MyData myData = new MyData();
        for (int i = 1; i <= 100; i++) {
            new Thread(() -> {
                try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); }
                for (int j = 1; j <= 100 ; j++) {
                    myData.addPlusPlus();
                }
            }, "T" + i).start();
        }
        while (Thread.activeCount() > 2) {

        }
        System.out.println(Thread.currentThread().getName() + "	 mission is over value:" + myData.number);
    }

    // 设置可见性
    private static void seeOkVisibility() {
        MyData myData = new MyData();
        new Thread(() -> {
            System.out.println(Thread.currentThread().getName() + "	 come in");
            try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); }
            myData.addTO60();
            System.out.println(Thread.currentThread().getName() + "	 updated number value: " + myData.number);
        }, "AAA").start();
        while (myData.number == 0) {

        }
        System.out.println(Thread.currentThread().getName() + "	 mission is over");
    }
}

class MyData {
    volatile int number;
    public void addTO60() {
        this.number = 60;
    }
    public void addPlusPlus() {
        this.number ++;
    }
}

ABA问题

/**
 * @desc AtomicReference ABA问题
 * @Author xw
 */
public class ABADemo {
    static AtomicReference<Integer> atomicReference = new AtomicReference<>(100);
    static AtomicStampedReference<Integer> atomicReference2 = new AtomicStampedReference<>(100, 1);

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

    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) + "	" + atomicReference.get() + "	" + atomicReference2.getStamp());
        }, "t2").start();
    }

    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) + "	" + atomicReference.get());
        }, "t2").start();
    }

}

DCL单例 + volatile（禁止指令重排）

/**
 * @desc DCL单例 + volatile（禁止指令重排）
 * @Date 2019/8/20
 */
public class SingletonDemo {
    private static volatile SingletonDemo instance = null;

    private SingletonDemo() {
        System.out.println(Thread.currentThread().getName() + "	 我是构造方法");
    }

    public static SingletonDemo getInstance() {
        if (instance == null) {
            synchronized (SingletonDemo.class) {
                if (instance == null) {
                    instance = new SingletonDemo();
                }
            }
        }
        return instance;
    }

    public static void main(String[] args) {
        for (int i = 1; i < 100; i++) {
            new Thread(() -> {
                try { TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { e.printStackTrace(); }
                SingletonDemo.getInstance();
            }, "T" + i).start();
        }
    }
}