This KB Article says that ASP.NET's Response.End()
aborts a thread.
Reflector shows that it looks like this:
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();
}
}
}
This seems pretty harsh to me. As the KB article says, any code in the app following Response.End()
will not be executed, and that violates the principle of least astonishment. It's almost like Application.Exit()
in a WinForms app. The thread abort exception caused by Response.End()
is not catchable, so surrounding the code in a try
…finally
won't satisfy.
It makes me wonder if I should always avoid Response.End()
.
Can anyone suggest, when should I use Response.End()
, when Response.Close()
and when HttpContext.Current.ApplicationInstance.CompleteRequest()
?
ref: Rick Strahl's blog entry.
Based on the input I've received, my answer is, Yes, Response.End
is harmful, but it is useful in some limited cases.
- use
Response.End()
as an uncatchable throw, to immediately terminate theHttpResponse
in exceptional conditions. Can be useful during debugging also. AvoidResponse.End()
to complete routine responses. - use
Response.Close()
to immediately close the connection with the client. Per this MSDN blog post, this method is not intended for normal HTTP request processing. It’s highly unlikely that you would have a good reason to call this method. - use
CompleteRequest()
to end a normal request.CompleteRequest
causes the ASP.NET pipeline to jump ahead to theEndRequest
event, after the currentHttpApplication
event completes. So if you callCompleteRequest
, then write something more to the response, the write will be sent to the client.
Edit – 13 April 2011
Further clarity is available here:
Best Answer
TL;DR
Per MSDN, Jon Reid, and Alain Renon:
ASP.NET Performance - Exception Management - Write Code That Avoids Exceptions
ThreadAbortException Solution
Response.End and Response.Close are not used in normal request processing when performance is important. Response.End is a convenient, heavy-handed means of terminating request processing with an associated performance penalty. Response.Close is for immediate termination of the HTTP response at the IIS/socket level and causes issues with things like KeepAlive.
The recommended method of ending an ASP.NET request is HttpApplication.CompleteRequest. Keep in mind that ASP.NET rendering will have to be skipped manually since HttpApplication.CompleteRequest skips the rest of the IIS/ASP.NET application pipeline, not the ASP.NET Page pipeline (which is one stage in the app pipeline).
Code
Copyright © 2001-2007, C6 Software, Inc as best I could tell.
Reference
HttpApplication.CompleteRequest
Response.End
Response.Close