.net - 什么可能导致进行 HttpWebRequest 调用的巨大开销？

Question

当我使用 HttpWebRequest(在 Silverlight 上)以小块形式发送/接收数据时，我测量了 500 字节/的非常小的吞吐量通过“本地主机”连接。当以大块发送数据时，我得到了 2 MB/s，这比 快了 5000 倍。

有谁知道什么会导致如此巨大的开销？

附加信息:

• 我正在使用 HTTP POST 方法
• 我在 Firefox 3.6 和 Internet Explorer 7 上进行了性能测量。两者的结果相似。
• 我的 CPU 只加载了 10%(四核，所以实际上是 40%)
• WebClient 显示了相似的结果
• WCF/SOAP showed similar results

更新:我使用的 Silverlight 客户端代码基本上是我自己实现的 WebClient 类。我写它的原因是因为我注意到 WebClient 存在相同的性能问题，并且我认为 HttpWebRequest 将允许调整性能问题。遗憾的是，这没有用。实现如下:

public class HttpCommChannel
{
    public delegate void ResponseArrivedCallback(object requestContext, BinaryDataBuffer response);

    public HttpCommChannel(ResponseArrivedCallback responseArrivedCallback)
    {
        this.responseArrivedCallback = responseArrivedCallback;
        this.requestSentEvent = new ManualResetEvent(false);
        this.responseArrivedEvent = new ManualResetEvent(true);
    }

    public void MakeRequest(object requestContext, string url, BinaryDataBuffer requestPacket)
    {
        responseArrivedEvent.WaitOne();
        responseArrivedEvent.Reset();

        this.requestMsg = requestPacket;
        this.requestContext = requestContext;

        this.webRequest = WebRequest.Create(url) as HttpWebRequest;
        this.webRequest.AllowReadStreamBuffering = true;
        this.webRequest.ContentType = "text/plain";
        this.webRequest.Method = "POST";

        this.webRequest.BeginGetRequestStream(new AsyncCallback(this.GetRequestStreamCallback), null);
        this.requestSentEvent.WaitOne();
    }

    void GetRequestStreamCallback(IAsyncResult asynchronousResult)
    {
        System.IO.Stream postStream = webRequest.EndGetRequestStream(asynchronousResult);

        postStream.Write(requestMsg.Data, 0, (int)requestMsg.Size);
        postStream.Close();

        requestSentEvent.Set();
        webRequest.BeginGetResponse(new AsyncCallback(this.GetResponseCallback), null);
    }

    void GetResponseCallback(IAsyncResult asynchronousResult)
    {
        HttpWebResponse response = (HttpWebResponse)webRequest.EndGetResponse(asynchronousResult);
        Stream streamResponse = response.GetResponseStream();
        Dim.Ensure(streamResponse.CanRead);
        byte[] readData = new byte[streamResponse.Length];
        Dim.Ensure(streamResponse.Read(readData, 0, (int)streamResponse.Length) == streamResponse.Length);
        streamResponse.Close();
        response.Close();

        webRequest = null;
        responseArrivedEvent.Set();
        responseArrivedCallback(requestContext, new BinaryDataBuffer(readData));
    }

    HttpWebRequest webRequest;
    ManualResetEvent requestSentEvent;
    BinaryDataBuffer requestMsg;
    object requestContext;
    ManualResetEvent responseArrivedEvent;
    ResponseArrivedCallback responseArrivedCallback;
}

我使用此代码将数据来回发送到 HTTP 服务器。

更新:经过大量研究，我得出结论 the performance problem is inherent to Silverlight v3 .

Answer 1

很可能您正在见证 Nagle 算法的效果，尝试:

this.webRequest.UseNagleAlgorithm.ServicePoint = false;

此外，Expect100Continue“握手”与 soap 服务调用性能相关:

this.webRequest.Expect100Continue.ServicePoint = false;

更新:

刚刚意识到 ServicePoint 在 Compact Framework 中不可用。但是，您可以通过以下方式证明这一点:

ServicePointManager.UseNagleAlgorithm = false

或者更改应用配置文件中的相关设置，或者 silverlight 中的任何等效设置？