What might cause the big overhead of making a HttpWebRequest call?
- by Dimitri C.
When I send/receive data using HttpWebRequest (on Silverlight, using the HTTP POST method) in small blocks, I measure the very small throughput of 500 bytes/s over a "localhost" connection. When sending the data in large blocks, I get 2 MB/s, which is some 5000 times faster.
Does anyone know what could cause this incredibly big overhead?
Update: I did the performance measurement on both Firefox 3.6 and Internet Explorer 7. Both showed similar results.
Update: The Silverlight client-side code I use is essentially my own implementation of the WebClient class. The reason I wrote it is because I noticed the same performance problem with WebClient, and I thought that the HttpWebRequest would allow to tweak the performance issue. Regrettably, this did not work. The implementation is as follows:
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;
}
I use this code to send data back and forth to an HTTP server.
