how to regenerate session id before expire in php code example

Example 1: php session regenerate id

<?php
session_start();

$old_sessionid = session_id();

session_regenerate_id();

$new_sessionid = session_id();

echo "Old Session: $old_sessionid<br />";
echo "New Session: $new_sessionid<br />";
?>

Example 2: php expire a session

//Ending a php session after 30 minutes of inactivity
$minutesBeforeSessionExpire=30;
if (isset($_SESSION['LAST_ACTIVITY']) && (time() - $_SESSION['LAST_ACTIVITY'] > ($minutesBeforeSessionExpire*60))) {
    session_unset();     // unset $_SESSION   
    session_destroy();   // destroy session data  
}
$_SESSION['LAST_ACTIVITY'] = time(); // update last activity