Login should not allow users to login if the application is logged in with the same login credentials

[Balasubramanyam A <knowledge.wealth@xxxxxxxxx>]

Hello,

I've written a simple application, where users need to login to access the
features of the application. I want to develop login system such that, if
user is already logged in, the application should not allow the users to
login with the same login credentials. How do I accomplish this?

Regards,
Balu