Problem about "sess_expiration"??

[eluser]Unknown[/eluser]
hello, I've problem when I use session to my php project.
now I want to UPDATE STATUS USER to OFFLINE when user is inactive for a while.

I think it might use session to update it so I test it following this

Code:

$config['sess_expiration'] = 30;

and I'm coding when session was null it will redirect to homepage. now it work. after 30 second it refresh perfectly.

then I insert code that update to database by reading

Code:

$this->userdata['mid']

that was USER ID that want to set to OFFLINE.
I test the function "setOffline($mid)" it can work.
then I add this function into "System/library/Session.php" in the first line of this function "function sess_destroy()" I think before clear session it must be updated database from session[USER ID] before. and I test it. it doesn't work. database won't update.

and I debug it until I delete all code in "function sess_destroy()" I think it will not redirect page again because sess_destroy fucntion is null. but!! it can delete session success after 30 second!! why session was delete successful I edit "sess_destroy()" to null??? or it cal other function when igniter want to delete session. I try to find all file but I can't found anywhere has variable "sess_expiration". so where do I insert update to database function when session was delete :'(

[eluser]WanWizard[/eluser]
It doesn't work that way.

Sessions expire because the cookie, that contains the session ID, expires. When the session library, in the constructor, doesn't detect the presence of the cookie, it will create a new session. The old one will remain in the database until the garbage collection process deletes it.