A similar function can be observed if you start performing a flow action on a case in one requester, and then attempt to perform a flow action on the same case from another requestor logged in as the same user.   The ootb behavior is to put up a screen telling you that another requestor already has the work locked, and giving you the option of killing that other requestor so the lock will be released.  Although this isn't exactly what you describe, if you use the Pega tracer to trace this ootb behavior, you can see how it is implemented, and base your design similarly.

Hi,

This is an expected behaviour for when there are Number of concurrent sessions allowed for each operator exceeded. For example the value is 2 then it will allow 2 times for operator and while attempting third time it won't decide/display which one need to kill.