Wordpress: Smart Wordpress Maintenance Mode

gistfile1.txt

<?php
/**
 * Place this file in root of wordpress site to enable
 * maintenance mode for users who are not logged in.
 * Also, allows access to /wp-admin during maintenance
 *
 * Filename: .maintenance
 */
function is_user_logged_in() {
    $loggedin = false;
    foreach ( (array) $_COOKIE as $cookie => $value ) {
        if ( stristr($cookie, 'wordpress_logged_in_') )
            $loggedin = true;
    }
    return $loggedin;
}
if ( ! stristr($_SERVER['REQUEST_URI'], '/wp-admin') && ! stristr($_SERVER['REQUEST_URI'], '/wp-login.php') && ! is_user_logged_in() )
    $upgrading = time();
?>