我使用jdk1.8。我认为没有volatile的双重检查锁是正确的。我多次使用Countdownlock测试，对象是singleton。如何证明它一定需要“易失性”
更新1
抱歉，我的代码没有格式化，因为我无法接收一些javascript公共类dcltest{

private static /*volatile*/ Singleton instance = null;

static class Singleton {

    public String name;

    public Singleton(String name) {
        try {
            //We can delete this sentence, just to simulate various situations
            Thread.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        this.name = name;
    }
}

public static Singleton getInstance() {
    if (null == instance) {
        synchronized (Singleton.class) {
            if (null == instance) {
                instance = new Singleton(Thread.currentThread().getName());
            }
        }
    }
    return instance;
}

public static void test() throws InterruptedException {
    int count = 1;
    while (true){
        int size = 5000;
        final String[] strs = new String[size];
        final CountDownLatch countDownLatch = new CountDownLatch(1);
        for (int i = 0; i < size; i++) {
            final int index = i;
            new Thread(()->{
                try {
                    countDownLatch.await();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                Singleton instance = getInstance();
                strs[index] = instance.name;
            }).start();
        }
        Thread.sleep(100);
        countDownLatch.countDown();
        Thread.sleep(1000);
        for (int i = 0; i < size-1; i++) {
            if(!(strs[i].equals(strs[i+1]))){
                System.out.println("i = " + strs[i] + ",i+1 = "+strs[i+1]);
                System.out.println("need volatile");
                return;
            }
        }
        System.out.println(count++ + " times");
    }
}

public static void main(String[] args) throws InterruptedException {
    test();
}

}