How to Prevent Concurrent User Logins in PHP/MySQL Site?

Question

I am developing the user management portion of a website that will host a webcast. The goal is to prrevent the same user nam (email address) from being used concurrently.

Answer 1

It's easy to determine when someone logs in. It's much harder to determine when someone logs out. If you have a mechanism of killing the webcast streaming to a particular user quickly, you might want to have something which pops up asking the user if they want to kill their other session if you think there might be one active.