End the current session and store session data.
Session data is usually stored after your script terminated without the need to call session_end(), but as session data is locked to prevent concurrent writes only one script may operate on a session at any time. When using framesets together with sessions you will experience the frames loading one by one due to this locking. You can reduce the time needed to laod all the frames by ending the session as soon as all changes to session variables are done.
See also: session_readonly().