设计模式 单例模式

    class Singleton
    {
        private static Singleton instance;
        private static readonly object syncRoot = new object();
        private Singleton()
        {
        }

        public static Singleton GetInstance()
        {
            if (instance == null)
            {

                lock (syncRoot)
                {

                    if (instance == null)
                    {
                        instance = new Singleton();
                    }
                }
            }
            return instance;
        }

    }