Something makes me think that this is a brainless question, but believe me, I really can't find a good solution for it. This should be a common problem, right ? For example, I could wish to limit the maximum number of concurrent accesses to 3 or 5 users on a peer-to-peer install, or to a greater number on a C/S install with SQL Server. But what should I do ?

I was thinking about a table of 'licensed' users with UserIds and Passwords, and a boolean field to check whether the user was already connected or not, but I admit that this doesn't seem too good. For example, if a connected machine crashes without closing the app, no changes would be reflected on the 'connected users' table...

What's the usual way to deal with this kind of issue ??