Question

Anybody know why ASP.NET might not abort the current thread with a Response.End()?

Update: Reason being that there is code, albeit not well written, that is getting executed after Response.End(). I’ve never seen a case where Response.End () didn’t stop the current thread from executing.

protected void Page_Load(object sender, EventArgs e)
{
        Response.Clear();
        Response.Redirect("somewhere", true);
        Response.End();

        //Some other code get's executed here
}

Answer 1

As you’ve pointed out, the method Response.End is defined as:

public void End()
{
  if (this._context.IsInCancellablePeriod) {
    InternalSecurityPermissions.ControlThread.Assert();
    Thread.CurrentThread.Abort(new HttpApplication.CancelModuleException(false));
  }
  else if (!this._flushing)
  {
    this.Flush();
    this._ended = true;
    if (this._context.ApplicationInstance != null) {
      this._context.ApplicationInstance.CompleteRequest();
    }
  }
}

Debugging a fairly simple web app with a break point in the Page_Load method, I can see the call stack includes the line:

System.Web.dll! System.Web.HttpApplication.ExecuteStep(System.Web.HttpApplication.IExecutionStep step = {System.Web.HttpApplication.CallHandlerExecutionStep}, ref bool completedSynchronously = true) + 0x4c bytes

Reflecting into CallHandlerExecutionStep I can see that the property IsCancellable is defined as:

bool HttpApplication.IExecutionStep.IsCancellable {
  get {
    return !(this._application.Context.Handler is IHttpAsyncHandler);
  }
}

The default handler for .aspx pages is the output from the PageHandlerFactory which implement IHttpHandler, not IHttpAsyncHandler – which would result in IsCancellable returning true (as indeed it does in my test app).

Have you configured a different HttpHandler in either your root web.config or one further up the stack to use an Async Handler instead? Are you using Update Panels with Partial Postbacks for example?