End of one session and Starting a new one?

PHP
1 
session_start();
session_regenerate_id();
session_destroy();
unset($_SESSION);
session_start();

or

session_start();
session_destroy();
unset($_SESSION);
session_start();

Are the above codes valid?

2

But do make sure you have session_start() at the top of every page that you wish to use sessions on.

3