Making WebRequests in parallel…

Under the assumption that making sequential WebRequests is slower than making them in parallel i wrote a little program that returns the HTTP status code for each URI in a list. Because the number of WaitHandles on a system is limited to 64 and i would have been required to hack around this limitation i decided to use ThreadPool instead…

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Net;

namespace ManyRequests
{
 class Program
 {
  static void Main(string[] args)
  {
   List<Uri> uris = new List<Uri>();
   uris.Add(new Uri("http://www.timvw.be"));
   uris.Add(new Uri("http://example.com/does_not_exist"));
   uris.Add(new Uri("http://www.timvw.be/c-sharp"));
   uris.Add(new Uri("http://www.timvw.be/rss-feed/"));
   uris.Add(new Uri("http://localhost"));

   Console.WriteLine("Getting the HttpStatusCodes...");
   HttpStatusCodeReader httpStatusCodeReader = new HttpStatusCodeReader(uris);
   int[] httpStatusCodes = httpStatusCodeReader.GetHttpStatusCodes();

   for (int i = 0; i < uris.Count; ++i)
   {
    Console.WriteLine("{0} {1}", httpStatusCodes[i], uris[i]);
   }

   Console.Write("{0}Press any key to continue…", Environment.NewLine);
   Console.ReadKey();
  }
 }

 public class HttpStatusCodeReader
 {
  private List<Uri> uris;
  private int[] httpStatusCodes;
  private object syncLock;
  private int completed;

  public HttpStatusCodeReader(List<Uri> uris)
  {
   if (uris == null)
   {
    throw new ArgumentNullException("uris");
   }

   foreach (Uri uri in uris)
   {
    if (uri.Scheme != Uri.UriSchemeHttp && uri.Scheme != Uri.UriSchemeHttps)
    {
     throw new ArgumentException(uri.ToString() + " is not valid http(s) uri.", "uris");
    }
   }

   this.uris = uris;
   this.httpStatusCodes = new int[uris.Count];
   this.syncLock = new object();
   this.completed = 0;
  }

  public int[] GetHttpStatusCodes()
  {
   for (int i = 0; i < this.httpStatusCodes.Length; ++i)
   {
    HttpWebRequest httpWebRequest = WebRequest.Create(this.uris[i]) as HttpWebRequest;
    httpWebRequest.Method = "HEAD";
    httpWebRequest.AllowAutoRedirect = true;
    httpWebRequest.BeginGetResponse(this.GetResponseCompleted, new object[] { httpWebRequest, i });
   }

   lock (this.syncLock)
   {
    while (this.completed < this.httpStatusCodes.Length)
    {
     Monitor.Wait(this.syncLock);
    }
   }

   return this.httpStatusCodes;
  }

  private void GetResponseCompleted(IAsyncResult ar)
  {
   object[] objects = ar.AsyncState as object[];
   HttpWebRequest httpWebRequest = objects[0] as HttpWebRequest;
   int index = (int)objects[1];

   HttpWebResponse httpWebResponse = null;

   try
   {
    httpWebResponse = httpWebRequest.EndGetResponse(ar) as HttpWebResponse;
    this.httpStatusCodes[index] = (int)httpWebResponse.StatusCode;
   }
   catch (WebException webException)
   {
    httpWebResponse = webException.Response as HttpWebResponse;
    if (httpWebResponse != null)
    {
     this.httpStatusCodes[index] = (int)httpWebResponse.StatusCode;
    }
   }
   finally
   {
    if (httpWebResponse != null)
    {
     httpWebResponse.Close();
    }

    lock (this.syncLock)
    {
     Interlocked.Add(ref this.completed, 1);
     Monitor.Pulse(this.syncLock);
    }
   }
  }
 }
}