java和C++之单例类双重检查加锁

1、Java

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

 

2、C++