Response.End（）不会中止当前线程

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?

Answer 2

You don't have it in a try block do you? That would throw a ThreadAbortException.

Answer 3

According to Community comment on http://msdn.microsoft.com/en-us/library/a8wa7sdt(VS.80).aspx (select .NET framework 2.0) the current thread is not cancellable in Global.asax:

"Careful!! If you pass true, Response.Redirect() calls Response.End(), however there are certain circumstances where Response.End() does not raise the ThreadAbortException and instead sets a couple of flags and returns. One such situation is when you're in Global.asax, but it would occur more generically in any execution step that was not cancellable. I'll add details on Response.End(), but in a page you'd be fine, but in Global.asax processing will continue even if you pass true as the second parm."

I actually noticed this behaviour in one of my projects.

Answer 4

I could be mistaken, but I believe for one thing the threads that are used are background threads that belong to a thread pool and are recycled so it doesn't kill the thread.

Response.End(), terminates the Response, but it doesn't return from the function.

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

        //Some other code get's executed here 
}