刮取一个网站内所有网页的最快方法

private string ScrapeWebpage(string url, DateTime? updateDate)
        {
            HttpWebRequest request = null;
            HttpWebResponse response = null;
            Stream responseStream = null;
            StreamReader reader = null;
            string html = null;

            try
            {
                //create request (which supports http compression)
                request = (HttpWebRequest)WebRequest.Create(url);
                request.Pipelined = true;
                request.KeepAlive = true;
                request.Headers.Add(HttpRequestHeader.AcceptEncoding, \"gzip,deflate\");
                if (updateDate != null)
                    request.IfModifiedSince = updateDate.Value;

                //get response.
                response = (HttpWebResponse)request.GetResponse();
                responseStream = response.GetResponseStream();
                if (response.ContentEncoding.ToLower().Contains(\"gzip\"))
                    responseStream = new GZipStream(responseStream, CompressionMode.Decompress);
                else if (response.ContentEncoding.ToLower().Contains(\"deflate\"))
                    responseStream = new DeflateStream(responseStream, CompressionMode.Decompress);

                //read html.
                reader = new StreamReader(responseStream, Encoding.Default);
                html = reader.ReadToEnd();
            }
            catch
            {
                throw;
            }
            finally
            {//dispose of objects.
                request = null;
                if (response != null)
                {
                    response.Close();
                    response = null;
                }
                if (responseStream != null)
                {
                    responseStream.Close();
                    responseStream.Dispose();
                }
                if (reader != null)
                {
                    reader.Close();
                    reader.Dispose();
                }
            }
            return html;
        }