/// <summary>
 /// 开始线程
 /// </summary>
 /// <param name="data"></param>
 public void DoWork(object data)
 {
     try
     {
         while (true)
         {
             if (_crawler.crawlRequests.Count == 0)
             {
                 Thread.Sleep(TimeSpan.FromSeconds(10));
                 continue;
             }
             CrawlRequest crawlRequest = null;
             lock (_crawler.crawlRequests)
             {
                 crawlRequest = _crawler.crawlRequests.Pop();
             }
             if (crawlRequest == null)
             {
                 Thread.Sleep(TimeSpan.FromSeconds(10));
                 continue;
             }
             try
             {
                 _logger.Debug($"begin request url[{crawlRequest.Url}]");
                 // 获取页面
                 HtmlWeb web = new HtmlWeb();
                 web.OverrideEncoding = Encoding.GetEncoding("gb2312");
                 var htmlDoc = web.Load(crawlRequest.Url);
                 crawlRequest.Callback(new CallbackEventArgs(crawlRequest.Url, htmlDoc, crawlRequest.Metadata, Name));
             }
             catch (Exception ex)
             {
                 _logger.Error(ex, $"request url[{crawlRequest.Url}]");
                 Thread.Sleep(TimeSpan.FromSeconds(5));
             }
         }
     }
     catch (Exception ex)
     {
         _logger.Error(ex, $"DoWork failed");
         // 线程被放弃
     }
 }