Best design pattern to adopt for chat system [closed]

I have a chat server that receives heartbeats from clients. The client passes inactive if the server didn't receive 3 consecutive heartbeats.

I have a chat groups, each group contains n members. If all members of a group become inactive, the group will be deleted.

In my opinion, I can use state and observer design patterns

State machine for members with states (active inactive) If the state become inactive the group will be updated/notified using observer design pattern.

What do you think? Any suggestions?

I have another question, how to declare the member inactive ?

My solution is to use a dedicated thread that compares the last received heartbeat for all members (1 thread for all members) The second solution is to create a thread per members that supervise that one.

Any comments?

Thanks