Most application server's I've worked with allow code to be 
executed when a session is garbage collected, making it 
easier to collect data about the sessions.

Would it be possible add a session_set_save_handler() type 
call that takes the same parameters with the difference 
that

- it'd accept null as a value so not all functions need to 
be defined
- this wouldn't stop PHP from executing the usual session 
handling
- the functions would be called with session data before 
the built in PHP handlers take effect

This would be very handy for creating statistics on page 
creation times as well as executing code upon garbage 
collection (storing session closure info) without having to 
write a complete implementation of session storage.

Also, session_garbage_collect() that forced collection and 
session_count() that returned the number of active sessions 
would be verry nice.