void PingServer(object state)
 {
     try
     {
         if (_client == null)
         {
             return;
         }
         _client.Ping();
         _pingTimer.Change(_pingDueTime, Timeout.Infinite);
     }
     catch (Exception ex)
     {
         _logger.Error("Ping Push Service失败, 出现异常", ex);
         _pingTimer.Change(Timeout.Infinite, Timeout.Infinite);
         StartWork();
     }
 }