I have an executable application that is run concurrently by multiple users on a Citrix server. My own knowledge of Citrix is zilch. I have been asked to determine if any given user attempts to run muliple - simultaneous - instances of the application (and if so, prevent that from happening).

I visualize some kind of system call that somehow identifies the user id within Citrix, so that if that user id is already active, I don't allow the app to execute. Can anyone tell me if such a system call exists? (I'm already aware of the Foxpro SYS call that tells me the user id within a desktop, but it seems to me that wouldn't work inside a Citrix environment. Is that correct?)

TIA
Howie