When an ASP.NET System.Web.HttpResponse.End() is called, the current thread is aborted?

Question

when a System.Web.HttpResponse.End() is called a System.Thread.Abort is being fired, which i'm guessing is (or fires) an exception? I've got some logging and this is being listed in the log file...

A first chance

exception of type 'System.Threading.ThreadAbortException' occurred in mscorlib.dll
12/14/2008 01:09:31::
Error in Path :/authenticate
Raw Url :/authenticate
Message :Thread was being aborted.
Source :mscorlib
Stack Trace :   at System.Threading.Thread.AbortInternal()
   at System.Threading.Thread.Abort(Object stateInfo)
   at System.Web.HttpResponse.End()
   at DotNetOpenId.Response.Send()
   at DotNetOpenId.RelyingParty.AuthenticationRequest.RedirectToProvider()
   at MyProject.Services.Authentication.OpenIdAuthenticationService.GetOpenIdPersonaDetails(Uri serviceUri) in C:\Users\Pure Krome\Documents\Visual Studio 2008\Projects\MyProject\Projects\Services\Authentication\OpenIdAuthenticationService.cs:line 108
   at MyProject.Mvc.Controllers.AuthenticationController.Authenticate() in C:\Users\Pure Krome\Documents\Visual Studio 2008\Projects\MyProject\Projects\MVC Application\Controllers\AuthenticationController.cs:line 69
TargetSite :Void AbortInternal()
A first chance exception of type 'System.Threading.ThreadAbortException' occurred in Ackbar.Mvc.DLL
An exception of type 'System.Threading.ThreadAbortException' occurred in Ackbar.Mvc.DLL but was not handled in user code

Is this normal behavior and is it possible to gracefully abort instead of (what looks like) a sudden abrupt abort?

Update

So far it the common census that it's by design. So i'm wondering if it's possible we could take this question and see if we could tweak the code to make it not feel like we're ending the thread prematurely and gracefully exit ... Possible? Code examples?

Answer 1

There is no such thing as a "graceful" abort. You could simply Flush() the response, though, instead of ending it and let the framework take care of closing the connection for you. I'm assuming in this case that you want the response sent to the client, i.e., the typical case.

According to MSDN, calling Response.End() throws the ThreadAbortException when the response ends prematurely. You really should only call Response.End() when you want the exception raised.

Answer 2

Yes, this is indeed by design. Microsoft has even documented it. How else would you stop the rest of your program from execution?

Answer 3

There's nothing inherently ungraceful about an exception recursing up your stack to stop the current execution. Certainly no more than you throwing an exception and catching it at some lower place in your exception.

I'd look at filtering it from your logging. If you're using the ASP.Net health monitoring you can configure/map each exception to a given provider (event log, mail, etc) to control whether you get a notification for threadabort exceptions or not. If it's custom logging then I'd just add an if to check for it.

Note that you can't eat a ThreadAbortException so even if your logging code is doing something like catch(Exception e) { // log exception and then do not throw again } the ThreadAbortException will still be raised again by the framework once your catch block exits.