searching across all open sessions

Is there any way (built in function or otherwise) to search for a value across all open sessions? Here's the problem: A user logs in, a new session is created and their user_id is saved as a session variable. 10 minutes later the same user logs in through a new second browser window, and another new session is created. If the user is using both browser windows, they may experience unexpected behavior since there may be session values from session1 that are not set or are different in the new session. What I would like to do is search across all open sessions for the user_id of anyone logging in and if their user_id is found then just assign this new browser their original sesssion id. Much thanks. Dave Krewet