public static function view_user_list($courseid) {
        global $CFG;
        require_once($CFG->dirroot . "/user/lib.php");
        require_once($CFG->dirroot . '/course/lib.php');

        $params = self::validate_parameters(self::view_user_list_parameters(),
                                            array(
                                                'courseid' => $courseid
                                            ));

        $warnings = array();

        if (empty($params['courseid'])) {
            $params['courseid'] = SITEID;
        }

        $course = get_course($params['courseid']);

        if ($course->id == SITEID) {
            $context = context_system::instance();
        } else {
            $context = context_course::instance($course->id);
        }
        self::validate_context($context);

        course_require_view_participants($context);

        user_list_view($course, $context);

        $result = array();
        $result['status'] = true;
        $result['warnings'] = $warnings;
        return $result;
    }