Question

All, I am trying to cancel two concurrent HttpWebRequests using a method similar to the code below (shown in pseudo-ish C#).

The Main method creates two threads which create HttpWebRequests. If the user wishes to, they may abort the requests by clicking a button which then calls the Abort method.

private Thread first;
private Thread second;
private string uri = "http://somewhere";

public void Main()
{
  first = new Thread(GetFirst);
  first.Start();

  second = new Thread(GetSecond);
  second.Start();

  // Some block on threads... like the Countdown class
  countdown.Wait();
}

public void Abort()
{
  try
  {
    first.Abort();
  }
  catch { // do nothing }

  try
  {
    second.Abort();
  }
  catch { // do nothing }
}

private void GetFirst(object state)
{
  MyHandler h = new MyHandler(uri);
  h.RunRequest();
}

private void GetSecond(object state)
{
  MyHandler h = new MyHandler(uri);
  h.RunRequest();
}

The first thread gets interrupted by a SocketException:

A blocking operation was interrupted by a call to WSACancelBlockingCall

The second thread hangs on GetResponse().

How can I abort both of these requests in a way that the web server knows that the connection has been aborted?, and/or, Is there a better way to do this?

UPDATE

As suggested, a good alternative would be to use BeginGetResponse. However, I don’t have access to the HttpWebRequest object – it is abstracted in the MyHandler class. I have modified the question to show this.

public class MyHandler
{
  public void RunRequest(string uri)
  {
    HttpWebRequest req = HttpWebRequest.Create(uri);
    HttpWebResponse res = req.GetResponse();
  }
}

Answer 1

Use BeginGetResponse to initiate the call and then use the Abort method on the class to cancel it.

http://msdn.microsoft.com/en-us/library/system.net.httpwebrequest_methods.aspx

I believe Abort will not work with the synchronous GetResponse:

http://msdn.microsoft.com/en-us/library/system.net.httpwebrequest.abort.aspx

If you have to stick with the synchronous version, to kill the situation, all you can do is abort the thread. To give up waiting, you can specify a timeout:

http://msdn.microsoft.com/en-us/library/system.net.httpwebrequest.timeout.aspx

If you need to kill the process, I would argue launching it inside a new AppDomain and dropping the AppDomain when you want to kill the request; instead of aborting a thread inside your main process.

Ignore the above, as @exaiwitmx below notes, Abort appears to work if called on a separate thread. That said, this may not be intended behaviour as should be tested accordingly.