WordPress - Add list of currently online users to admin bar

WP - Online Users

/*
* Apply online user status
*/
function gr_users_online_transient() {
  if ( is_user_logged_in() ) {
		$key    = 'online';
		$time   = 60 * 5;
		$user   = wp_get_current_user();
		$id     = $user->ID;
		$status = get_transient( $key .'_'. $id );
		if ( empty( $status ) ) {
			$status = 'online';
			set_transient( $key .'_'. $id, $status, $time );
		}
	}
}
add_action( 'init', 'gr_users_online_transient' );
class gr_users_online_menu {
	function gr_users_online_menu() {
		add_action( 'admin_bar_menu', array( $this, "gr_users_online_menu_links" ), 90 );
	}
	function add_root_menu($name, $id, $href = FALSE) {
		global $wp_admin_bar;
		if ( !is_super_admin() || !is_admin_bar_showing() ) {
			return;
		}
		$wp_admin_bar->add_menu( array(
			'id'    => $id,
			'meta'  => array(),
			'title' => $name,
			'href'  => $href )
		);
	}
	function add_sub_menu($name, $link, $root_menu, $id, $meta = FALSE) {
		global $wp_admin_bar;
		if ( ! is_super_admin() || ! is_admin_bar_showing() ) {
			return;
		}    
		$wp_admin_bar->add_menu( array(
			'parent' => $root_menu,
			'id'     => $id,
			'title'  => $name,
			'href'   => $link,
			'meta'   => $meta
		));
	}
	function gr_users_online_menu_links() {
		$num   = 0;
		$users = get_users('orderby=nicename');
		foreach ( $users as $user ) {
			$status = get_transient( 'online_'. $user->ID );
			if ( $status == 'online' ) {
				$data = get_userdata( $user->ID );
				$this->add_sub_menu( $data->display_name, '', 'gr-user', 'gr-user-'. $user->ID );
				++$num;
			}
		}
		if ( $num > 1 ) {
			$this->add_root_menu( $num .' '. __('online users','green'), 'gr-user' );
		}
	}
}
function gr_users_online_init() {
	global $gr_users_online_menu;
	$gr_users_online_menu = new gr_users_online_menu();
}
add_action( 'init', 'gr_users_online_init' );