下载管理器 - 限制下载速度 [重复]

Question

我需要为我的文件下载器应用程序实现下载速率限制，我查看了 CodeProject 中的 ThrottledStream 类，但这不适用于我的情况，因为我必须能够更改限制在下载期间，而不仅仅是在开始时。这是我在后台线程中使用的下载方法的一部分：

webResponse = (HttpWebResponse)webRequest.GetResponse();
responseStream = webResponse.GetResponseStream();
responseStream.ReadTimeout = 5000;

downloadCache = new MemoryStream(this.MaxCacheSize);
byte[] downloadBuffer = new byte[this.BufferSize];
int bytesSize = 0;
CachedSize = 0;
int receivedBufferCount = 0;

while (true)
{
    bytesSize = responseStream.Read(downloadBuffer, 0, downloadBuffer.Length);

    if (this.Status != DownloadStatus.Downloading || bytesSize == 0 
        || this.MaxCacheSize < CachedSize + bytesSize)
    {
        WriteCacheToFile(downloadCache, CachedSize);

        this.DownloadedSize += CachedSize;
        downloadCache.Seek(0, SeekOrigin.Begin);
        CachedSize = 0;

        if (this.Status != DownloadStatus.Downloading || bytesSize == 0)
            break;
    }

    downloadCache.Write(downloadBuffer, 0, bytesSize);
    CachedSize += bytesSize;

    receivedBufferCount++;
    if (receivedBufferCount == this.BufferCountPerNotification)
    {
        this.RaiseDownloadProgressChanged();
        receivedBufferCount = 0;
    }
}

我也看到有人使用 Thread.Sleep() 或 Thread.Wait()，但这是个好主意吗？你有什么建议我可以在这个while循环中做到这一点吗？

Answer 1

我已经使用此代码从服务器下载文件可能对您有帮助...

   private bool DownLoadFile(string pstrFileName, string pstrFilePath, long plngFileSize)
    {
        try
        {
            string strNewFileSize = CalcFileSize(plngFileSize);
            int numIterations = 0;  // this is used with a modulus of the sampleInterval to check if the chunk size should be adjusted.  it is started at 1 so that the first check will be skipped because it may involve an initial delay in connecting to the web service
            Offset = 0;
            long webConfigSetting = this.mobjService.GetMaxRequestLength();
            this.MaxRequestLength = Math.Max(1, (webConfigSetting * 1024) - (2 * 1024));    // set the max buffer size to slightly less than the request length to allow for SOAP message headers etc.  
            if (File.Exists(pstrFilePath))
            {
                Offset = new FileInfo(pstrFilePath).Length;
                if (Offset == plngFileSize)
                    Offset = 0;
                //File.Delete(pstrFilePath);
            }
            if (Offset == 0 && !File.Exists(pstrFilePath))   // create a new empty file
                File.Create(pstrFilePath).Close();

            // open a file stream for the file we will write to in the start-up folder
            lblFileName.Text = pstrFileName.Substring(0, pstrFileName.LastIndexOf(".")).Replace("&", "&&");
            using (FileStream fs = new FileStream(pstrFilePath, FileMode.OpenOrCreate, FileAccess.Write))
            {
                pbrSummary.Maximum = (int)plngFileSize;
                fs.Seek(Offset, SeekOrigin.Begin);
                // download the chunks from the web service one by one, until all the bytes have been read, meaning the entire file has been downloaded.
                while (Offset < plngFileSize)
                {
                    int currentIntervalMod = numIterations % this.ChunkSizeSampleInterval;
                    if (currentIntervalMod == 0)
                        StartTime = DateTime.Now;   // used to calculate the time taken to transfer the first 5 chunks
                    else if (currentIntervalMod == 1)
                        CalcAndSetChunkSize(plngFileSize);
                    try
                    {
                        // although the DownloadChunk returns a byte[], it is actually sent using MTOM because of the configuration settings. 
                        byte[] Buffer = mobjService.DownloadChunk(pstrFileName, Offset, ChunkSize);
                        fs.Write(Buffer, 0, Buffer.Length);
                        Offset += Buffer.Length;    // save the offset position for resume
                    }
                    catch (Exception ex)
                    {
                        if (ex.Message.Contains("File not found") || NumRetries++ >= MaxRetries)    // too many retries, bail out
                        {
                            fs.Close();
                            return false;
                            //throw new Exception("Error occurred during upload, too many retries.\r\n" + ex.Message);
                        }
                    }
                    numIterations++;
                    //----------------------- Code Commented ------------------------
                    //lblDownload.Text = CalcFileSize(Offset) + " of " + strNewFileSize;
                    //lblRate.Text = CalcFileSize(ChunkSize)+"/sec";
                    ////pbrSummary.Value = (int)Offset;
                    ////if ((int)Offset <= pbrSummary.Maximum)
                    ////    pbrSummary.Value = (int)Offset;
                    ////else
                    ////    pbrSummary.Value = pbrSummary.Maximum;
                    //------------------------------------------------------------------
                }
            }
            return true;
        }
        catch (Exception Exc)
        {
            throw (Exc);
        }
    }
    private void CalcAndSetChunkSize(long plngFileSize)
    {
        /* chunk size calculation is defined as follows 
         *      in the examples below, the preferred transfer time is 1500ms, taking one sample.
         *      
         *                                    Example 1                                 Example 2
         *      Initial size                = 16384 bytes   (16k)                       16384
         *      Transfer time for 1 chunk   = 800ms                                     2000 ms
         *      Average throughput / ms     = 16384b / 800ms = 20.48 b/ms               16384 / 2000 = 8.192 b/ms
         *      How many bytes in 1500ms?   = 20.48 * 1500 = 30720 bytes                8.192 * 1500 = 12228 bytes
         *      New chunksize               = 30720 bytes (speed up)                    12228 bytes (slow down from original chunk size)
         */
        double transferTime = DateTime.Now.Subtract(this.StartTime).TotalMilliseconds;
        double averageBytesPerMilliSec = this.ChunkSize / transferTime;
        double preferredChunkSize = averageBytesPerMilliSec * this.PreferredTransferDuration;
        this.ChunkSize = (int)Math.Min(this.MaxRequestLength, Math.Max(4 * 1024, preferredChunkSize)) * 10; // set the chunk size so that it takes 1500ms per chunk (estimate), not less than 4Kb and not greater than 4mb // (note 4096Kb sometimes causes problems, probably due to the IIS max request size limit, choosing a slightly smaller max size of 4 million bytes seems to work nicely)         

        //string statusMessage = String.Format("Chunk size: {0}{1}", CalcFileSize(this.ChunkSize), (this.ChunkSize == this.MaxRequestLength) ? " (max)" : "");
    }