关于单例模式

单例模式是为了使一个类只有一个实例，并提供一个全局访问点--抄的


 public class SingleInstance<T> where T:class,new()
    {
        private static T _instance;
        private static readonly object lock= new object();

        public static T getInstance()
        {
            if (_instance == null)
            {
                lock (lock)
                {
                    if (_instance == null)
                    {
                        _instance = new T();
                    }
                    
                }
            }
            return _instance;
        }
    }

第一个if是为了同步访问时没必要每次都加锁，浪费资源；