note 15767 rejected from ref.session by zak

I am building a chat/message system in php. My question is : How can you now that a session ends and then take the appropriate actions ? For instance when a user closes his browser while a session is open. I've tried using the javascript onUnload event handler but this doesn't seem to work on all systems. In asp there's a global.asa file where you can define session_on_start and session_on_end event handlers. Is there functionality like this in php ? tnx & greetz, jan