End the current session and store session data.
Session data is usually stored after your script
terminated without the need to call
session_write_close(), 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 load
all the frames by ending the session as soon as all changes
to session variables are done.