C#---- 单列模式（定时器）

 // 定义计时器对象
 1  public class CountDown
    {

        private static CountDown theCountDown = null;
        private static readonly object _padLock = new object(); // unique object for lock

        private Timer timer = null; //计时器
        private int dt;

        /// <summary>
        /// decide logic
        /// </summary>
        public int DT
        { 
            get;
            set;
        }           

        private CountDown ()
        {
            timer = new Timer();
            timer.Interval = 60000;  // 1 min to elapsed 
            dt = 0;
            DT = 0; 
            timer.Elapsed += timer_Elapsed;            
        }

       private void timer_Elapsed(object sender, ElapsedEventArgs e)
        {
            dt--;
            if (dt<=0)
            {
                timer.Stop();                
            }
            DT = dt; // update DT for logic
        }


        /// <summary>
        /// start timer by using param to set times of loop
        /// </summary>
        /// <param name="times"></param>
        public void Start(int times)
       {
            if (dt <=0)
            {
                dt = times;
                timer.Start();
            }
          
       }

        /// <summary>
        /// start timer 60 times loop as default
        /// </summary>
        public void Start()
        {
            if (dt <= 0)
            {
                dt = 60;
                timer.Start();
            }

        }

        /// <summary>
        /// stop  timer
        /// </summary>
        public void Stop()
        {
            timer.Stop();
        }            

        /// <summary>
        ///  实例化定时器
        /// </summary>
        /// <returns></returns>
        public static CountDown Instance()
        {
            //判定对象是否实例化
            if (null == theCountDown)
            {
                lock (_padLock)// 添加线程锁
                {
                    if (null == theCountDown)
                    {
                        theCountDown = new CountDown();
                    }
                }

            }
            return theCountDown;
        }
    }

  //实例化对象
                CountDown cd = CountDown.Instance();
                if (cd.DT <= 0)
                {  

                    // TODO Something：

                    cd.Start(60); //开始计时，设定循环次数（1小时后，才可以再次调用该逻辑）
                }