It might be useful to be able to limit the number of concurrent users. This has nothing to do with licensing, but might be useful anway. For example, a system administrator might want to reduce the server load. It should be easy to implement this, since the vsmserver already has knowledge of the number of concurrent users. All we need to do is to add a parameter to vsmserver.conf, and use it in vsmserver.
To be useful, this should probably be settable *per*agent*; not per cluster. That's a bit harder than just checking this on the VSM server. Perhaps not very useful after all. Re-targeting.
*** Bug 5966 has been marked as a duplicate of this bug. ***
Also note bug 4429 which may remove some of the need for this feature, depending on how it turns out.
A use case that's been described to us is users making heavy use of GPUs. The amount of RAM is a limiting factor and many applications are designed to get exclusive access and don't gracefully deal with memory running out. So our users want to work around this by limiting the number of users per agent, and hence per GPU. In some cases to the extreme of one user per agent. For them it is a better user experience to be denied a session than applications crashing or erroring out.
Another use case is security, where the admin wants to minimize the risk of data leaking between users by only having a single user per system. Note that this assumes that there is no substantial risk of things being left behind by a user as an agent can be reused for a different user once the first user logs out.