global component to manage current users

[wh]

The application that I'm about to start working on requires maintaining a
list of users currently accessing an asp.net application running on IIS5.0.

I essentially need to monitor which xml files on the server various users
are working on. When a user selects an xml file, it is marked as 'locked'
thus disallowing other users from modifying it. The users will come and go
and I therefore need to remove the 'locked' flag from the respective xml
files they were working on. (I assume I can add code to the Session_OnEnd
event to remove locks from files caused by users not logging out properly).

The number of users in the system is expected to be very few at a single
time (maximum of 3).

My idea is to have a global object that can be accessed by users from other
sessions. It would provide an interface something similar to:

myobject.LockXm lFile()
myobject.ReadXm lFile()
myobject.Unlock XmlFile()

The object would then keep track of what xml file is being used by each user
(via the Session ID). My question is what issues would I need to look at in
terms of multiple pages accessing the global object at a single time? I
understand that the component needs to be free threaded. Presumably I'd need
to perform all locking inside the component to ensure there are no race
conditions. Do I need to 'mark' the component as free threaded or does .Net
assume that it is free threaded?

I plan to create an instance of the global object in the
Application_OnS tart() event and store it in the HttpApplication State object
via the Application variable. I am aware that upon processing a request, the
HttpRuntime selects an HttpApplication object from a resource pool. Would
the global object I am creating be accessible from other HttpApplication
objects used by requests from other users? All requests are being accessed
in the same worker process though on different threads so I don't see a
problem there - am I correct?

Wayne.