private KeepAlive(string applicationUrl)
 {
     _applicationUrl = applicationUrl;
     _cacheKey       = Guid.NewGuid().ToString();
     instance        = this;
     PingCount       = 0;
 }
 public static void Stop()
 {
     lock (sync)
     {
         HttpRuntime.Cache.Remove(instance._cacheKey);
         instance = null;
     }
 }
 public static void Start(string applicationUrl)
 {
     if (IsKeepingAlive)
     {
         return;
     }
     lock (sync)
     {
         instance = new KeepAlive(applicationUrl);
         instance.Insert();
     }
 }