.NET上传文件有线程限制？？

有问有答是美德！

发下主要代码，请大家帮忙看下原因，谢谢。。。
                ObjectMetadata metadata = new ObjectMetadata();
                metadata.ContentType = "application/file";
                ClientConfiguration config = new ClientConfiguration();
                config.ConnectionTimeout = -1; 
                OssClient ossClient = new OssClient(new Uri("http://oss.aliyuncs.com"), AccessID, AccessKey, config);

                //单文件上传
                //fs = File.Open(FileToUpload, FileMode.Open);
                //PutObjectResult Result = ossClient.PutObject(Bucket, Key, fs, metadata);

                InitiateMultipartUploadRequest initRequest = new InitiateMultipartUploadRequest(Bucket, Key);
                InitiateMultipartUploadResult initResult = ossClient.InitiateMultipartUpload(initRequest);

                // 设置每块大小
                int partSize = 1024 * 1024 * 3;

                FileInfo partFile = new FileInfo(FileToUpload);
                FileSize = partFile.Length;

                // 计算分块数目
                int partCount = (int)(partFile.Length / partSize);
                if (partFile.Length % partSize != 0)
                {
                    partCount++;
                }

                for (int i = 0; i < partCount; i++)
                {
                    // 获取文件流
                    FileStream fis = new FileStream(partFile.FullName, FileMode.Open,FileAccess.Read);
                    
                    // 跳到每个分块的开头
                    long skipBytes = partSize * i;
                    fis.Position = skipBytes;

                    // 计算每个分块的大小
                    long size = partSize < partFile.Length - skipBytes ?
                            partSize : partFile.Length - skipBytes;

                    // 创建UploadPartRequest，上传分块
                    UploadPartRequest uploadPartRequest = new UploadPartRequest(Bucket, Key, initResult.UploadId);
                    uploadPartRequest.InputStream = fis;
                    uploadPartRequest.PartSize = size;
                    uploadPartRequest.PartNumber = (i + 1);

                    BackgroundWorker bw = new BackgroundWorker();
                    bw.WorkerReportsProgress = true;
                    bw.DoWork += new DoWorkEventHandler(bw_DoWork);
                    bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
                    bw.RunWorkerAsync(new object[] { ossClient, uploadPartRequest, partCount, fis, i + 1 });
                    Thread.Sleep(500);

        //线程工作
        void bw_DoWork(object sender, DoWorkEventArgs e)
        {
            object[] args = e.Argument as object[];
            OssClient ossClient = args[0] as OssClient;
            UploadPartRequest uploadPartRequest = args[1] as UploadPartRequest;
            int partCount = int.Parse(args[2].ToString());
            FileStream fis = args[3] as FileStream;
            int partNumber = int.Parse(args[4].ToString());

            long startPosition = fis.Position;
            //实例化watcher对象，用于监视进度、速度、剩余时间，并加入列表
            UploadWatcher watcher = new UploadWatcher() { partNumber = partNumber, startPosition = startPosition, uploadPosition=startPosition, fis = fis };
            itemList.Add(watcher);

            UploadPartResult uploadPartResult = ossClient.UploadPart(uploadPartRequest);  
            partETags.Add(uploadPartResult.PartETag);
            threadDoneCount += 1;
            e.Result = new object[] { ossClient, uploadPartRequest.UploadId, partCount };
            UploadSize += ((long)uploadPartRequest.PartSize);
        }


        //线程完成
        void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            object[] args = e.Result as object[];
            OssClient ossClient = args[0] as OssClient;
            string UploadId = args[1] as string;
            int partCount = int.Parse(args[2].ToString());
            //当最后一个线程执行完毕时，进行分块文件的合并
            if (threadDoneCount == partCount)
            {
                CompleteMultipartUploadRequest completeReq = new CompleteMultipartUploadRequest(Bucket, Key, UploadId);
                //对分块上传的返回信息按PartNumber排序，因为合并时要求必须是升序
                var query = from q in partETags
                            orderby q.PartNumber ascending
                            select q;
                List<PartETag> sortedPartETags = query.ToList<PartETag>();
                foreach (PartETag partETag in sortedPartETags)
                {
                    completeReq.PartETags.Add(partETag);
                }
                CompleteMultipartUploadResult completeResult = ossClient.CompleteMultipartUpload(completeReq);
                UploadFilish = true;
                UploadOK = true;
                State = UploadState.done;
            }
        }

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呃，解决了。SDK没有问题，是忘记设置.net的HttpRequest并发限制了，xp、win7默认限制都是2个。。。