At server side,there is a session object,
such as page.session,httpcontext.session, that's all the same thing.
When the request reached the web server, IIS load the Aspnet_ISAPI.Dll,
then the aspnet_wp.exe is loaded, then appdomain is created, and then
httpcontext is created.
I want to know when the session object is created at server side and which
object create it.