In IIS7, what happens between Application_BeginRequest and Application_PreRequestHandlerExecute?

Question

I've got some tracing statements with timestamps on an ASP.Net IIS application that gets a lot of traffic. I've got trace statements at the end of Application_BeginRequest and the beginning of Application_PreRequestHandlerExecute in my Global.asax. Occasionally there is a big delay between the end of BeginRequest and the start of PreRequestHandlerExecute, i.e. more than 5 seconds.

What is going on in the lifecycle of an HttpRequest between these two method calls that could be taking so long? This is IIS7 on Windows Server 2008.

Thanks.

Answer 1

If BeginRequest has already happend and the delay is before PreRequestHandlerExecute, you might want to log the thread id. If it is different, you suffer from ASP.NET thread agility.

A reason for this to happen can be the use of sessions. ASP.NET uses a reader-writer lock on the HttpContext.Current.Session. If you write to this variable, all the other request with the same session cannot run concurrently and are parked in a queue. .NET uses a polling mechanism to check whether the session lock is released.

I would also recommend checken that you've build on Release and that system.web/compilation/@debug = 'false'