public class CountdownHelper
  {
     private const int CacheSlidingExpirationHour = 2;
     private const string CountdownCurrentIndexCacheName = "OnlineMeetingCountdownCurrentIndex";
     private static IAppLog log = AppLoggerManager.GetLogger(typeof(CountdownHelper));
     private static Cache m_cache = HttpContext.Current.Cache;
     private static object m_objCountdownCurrentIndexLock = new object();
     private static int[] m_snIntervalSecond = new int[] { 0, 1 , 1 , 1}; //1显示 0不显示
 
     public CountdownHelper()
     {
     }

     public int GetCountdownAddedSecond()
     {
       lock (m_objCountdownCurrentIndexLock)
       {
         int nCountdownCurrentIndex = 0;
 
         try
         {
           object objCountdownCurrentIndex = m_cache[CountdownCurrentIndexCacheName];
           if (objCountdownCurrentIndex == null)
           {
             //如果需要加缓存的，就用下面的
             //m_cache.Insert(CountdownCurrentIndexCacheName, 1, null, Cache.NoAbsoluteExpiration, TimeSpan.FromHours(CacheSlidingExpirationHour), CacheItemPriority.NotRemovable, null);
             //不用加缓存的用下面的
             m_cache.Insert(CountdownCurrentIndexCacheName, 1, null, Cache.NoAbsoluteExpiration, Cache.NoSlidingExpiration, CacheItemPriority.NotRemovable, null);
           }
           else
           {
             nCountdownCurrentIndex = (int)objCountdownCurrentIndex;

             if (nCountdownCurrentIndex == m_snIntervalSecond.Length - 1)
             {
               m_cache[CountdownCurrentIndexCacheName] = 0;
             }
             else
             {
               m_cache[CountdownCurrentIndexCacheName] = nCountdownCurrentIndex + 1;
             }
           }
 
           return m_snIntervalSecond[nCountdownCurrentIndex];
        }
        catch (Exception __error)
         {
           //如果需要记录错误日志的，可以记录到这里，我这里没有加
           //log.Error("功能介绍GetCountdownAddedSecond：" + __error.Message);
           if (nCountdownCurrentIndex > m_snIntervalSecond.Length - 1)
           {
             nCountdownCurrentIndex = m_snIntervalSecond.Length - 1;
          }
           return m_snIntervalSecond[nCountdownCurrentIndex];
         }
       }
     }
 
   }

1 <div id="adver"></div>

<!--轮询曝光-->
   $.post("/Topic/GetCountdownAddedSecond", function (data) {
    if (data) {
       if (data.num == 1) {
        var img_html = "<img src=\"https://d_directed_treatment =?\ment\" style=\"display:none;\">";
         $("#adver").html(img_html);
       }
     }
   }, "json");