单例模式与多线程

    class Singleton   //延迟加载，这种实现在多线程中存在线程安全的问题
    {
        private static Singleton _instance;

        public static Singleton getSingleton()
        {
            if (_instance == null)
            {
                _instance = new Singleton();
            }
            return _instance;
        }
    }

    class Singleton_DoubleCheckedLocked
    {
        private static Singleton_DoubleCheckedLocked _instance;
        public static Singleton_DoubleCheckedLocked getSingleton()
        {
            if (_instance == null)
            {
                lock (this)  //lock锁的对象必须为引用类型的(字符串除外)且最好不要是public类型对象
                {
                    if (_instance == null)
                    {
                        _instance = new Singleton_DoubleCheckedLocked();
                    }
                }
            }
            return _instance;
        }
    }

    class SingletonAutoInitial //非延迟加载
    {
        private static SingletonAutoInitial _instance = new SingletonAutoInitial();
        public static SingletonAutoInitial getSingleton()
        {
            return _instance;
        }
    }