public static function getInstance($id = null, $phpExecutable = 'php', $tmpPath = 'tmp/')
    {
        if (is_null(self::$_instance)) {
            self::$_phpExecutable = $phpExecutable;
            self::$_tmpPath = $tmpPath;

            $jobRunner = new JobRunner($id);
            self::$_instance = $jobRunner;
        }

        return self::$_instance;
    }