dotNet 自带线程池与HTTP访问的若干疑问

疑问:

1. 用HttpWebResponse的同步方式, 配合.NET自带的线程池, 从WEB上获取数据, 运行一段时间后, 被阻塞的线程会越来越多, 直到所有任务全部完成, 那些被阻塞的线程才会全部退出(自动)

2. 用HttpWebResponse的异步方式,直接产生大量任务(1w个), 则大约有20%的任务没有被处理, 而程序任务已经全部处理完毕.

针对上述2种情况, 换用SmartThreadPool来实现同样1w个任务, 则没有任何问题, 线程数稳定在40左右, 而且所有任务都完成了(发生异常,也算是执行了任务)

        public static object Download1(object o)
        {
            HttpWebResponse response = null;
            Stream ReceiveStream = null;
            FileStream fs = null;
            BinaryWriter w = null;
            string ID = string.Empty;
            try
            {
                byte[] nbytes = new byte[512];
                DownFileArg arg = o as DownFileArg;
                ID = arg.ID;
                DownFileStat.AddTask(arg.ID);
                string FILE_NAME = arg.FileName;
                String PathInfo = arg.TargetPath + "\\" + FILE_NAME;
                if (File.Exists(PathInfo))
                {
                    FileInfo fi = new FileInfo(PathInfo);
                    if (fi.Length > 0)
                    {
                        //Console.WriteLine("File {0} Exists!", FILE_NAME);
                        return null;
                    }
                }

                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(arg.PicURL);
                request.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; SV1; .NET CLR 2.0.50727; TheWorld)";
                request.Timeout = 20000;
                response = (HttpWebResponse)request.GetResponse();
                if (response.ContentType.IndexOf("image") < 0)
                {
                    //返回的不是图片数据
                    //是否需要抛异常?
                    return null;
                }
                ReceiveStream = response.GetResponseStream();
                fs = new FileStream(PathInfo, FileMode.Create);
                w = new BinaryWriter(fs);
                int nreadsize = ReceiveStream.Read(nbytes, 0, 512);
                while (nreadsize > 0)
                {
                    w.Write(nbytes, 0, nreadsize);
                    nreadsize = ReceiveStream.Read(nbytes, 0, 512);
                }


            }
            catch (WebException webExcp)
            {
                // Get the WebException status code.
                WebExceptionStatus status = webExcp.Status;
                // If status is WebExceptionStatus.ProtocolError, 
                //   there has been a protocol error and a WebResponse 
                //   should exist. Display the protocol error.
                if (status == WebExceptionStatus.ProtocolError)
                {
                    // Get HttpWebResponse so that you can check the HTTP status code.
                    HttpWebResponse httpResponse = (HttpWebResponse)webExcp.Response;
                    ExceptionHelper.Write("The server returned protocol error " + ID + " " + (int)httpResponse.StatusCode + " - " + httpResponse.StatusCode);
                }
            }
            catch (Exception e)
            {
                ExceptionHelper.Write(ID + " " + e.Message);
            }
            finally
            {
                DownFileStat.FinishTask(ID);
                if (response != null)
                {
                    response.Close();
                }
                if (w != null)
                {
                    w.Close();
                }

                if (ReceiveStream != null)
                {
                    ReceiveStream.Close();
                }
                if (fs != null)
                {
                    fs.Close();
                }

            }
            return null;
        }

    public class DownFileArg
    {
        private string _picURL;

        public string PicURL
        {
            get { return _picURL; }
        }
        private string _ID;

        public string ID
        {
            get { return _ID; }
        }
        private string _TargetPath;

        public string TargetPath
        {
            get { return _TargetPath; }
        }

        private string _fileName;

        public string FileName
        {
            get { return _fileName; }
        }

        public DownFileArg(string jpgurl, string ID, string targetPath, string filename)
        {
            _picURL = jpgurl;
            _ID = ID;
            _TargetPath = targetPath;
            _fileName = filename;
        }

(To be continued)