C#设计模式--单例模式

    /// <summary>
    /// 私有化构造函数
    /// </summary>
    public class Singleton
    {
        private Singleton()
        {//构造函数可能耗时间，耗资源

        }
        public static Singleton CreateInstance()
        {
            if (_Singleton == null)
            {
                _Singleton = new Singleton();
            }
            return _Singleton;
        }
    }

    /// <summary>
    /// 私有化构造函数
    /// 私有静态变量保存对象
    /// </summary>
    public class Singleton
    {

        private Singleton()
        {//构造函数可能耗时间，耗资源

        }

        private static Singleton _Singleton = null;
        private static readonly object locker = new object();//加锁
        //双if加lock
        public static Singleton CreateInstance()
        {
            if (_Singleton == null)//保证对象初始化之后不需要等待锁
            {
                lock (locker)//保证只有一个线程进去判断
                {
                    if (_Singleton == null)
                    {
                        _Singleton = new Singleton();
                    }
                }
            }
            return _Singleton;
        }
    }

    public class SingletonSecond
    {

        private SingletonSecond()
        {//构造函数可能耗时间，耗资源
          
        }
     
        private static SingletonSecond _Singleton = null;
        static SingletonSecond()//静态构造函数，由CLR保证在第一次使用时调用，而且只调用一次
        {
            _Singleton = new SingletonSecond();
        }
        public static SingletonSecond CreateInstance()
        {
            return _Singleton;
        }
    }

 public class SingletonThird
    {

        private SingletonThird()
        {//构造函数可能耗时间，耗资源
           
        }
       
        private static SingletonThird _Singleton = new SingletonThird();
        public static SingletonThird CreateInstance()
        {
            return _Singleton;
        }
    }