public void SaveUrlPics(string url, string path, Random ran)
        {
            WebClient wc = new WebClient();
            
            string address = path + "\\" + CreateRandomCode(8) + GetSuffix(path);
            try
            {
//在这里我想把当前线程等待
                wc.DownloadFile(url, address);

                wc.DownloadFileCompleted += new System.ComponentModel.AsyncCompletedEventHandler(wc_DownloadFileCompleted);
            }
            catch (Exception ex)
            {
                ListUrl.writeLog(ex.Message);
            }
            finally
            {
                wc.Dispose();
            }
        }

        void wc_DownloadFileCompleted(object sender, System.ComponentModel.AsyncCompletedEventArgs e)
        {
            //下载完成后，放走线程。
        }