public function runProcess($output_file = '/dev/null', $append = false)
    {
        switch (PHP_OS) {
            case 'Windows':
                shell_exec(sprintf('%s &', $this->function_code, $output_file));
                break;
            case 'Linux':
                $this->pid = (int)shell_exec(sprintf('php -r "%s" %s %s 2>&1 & echo $!', str_replace('"', '\"', $this->function_code), ($append) ? '>>' : '>', $output_file));
                break;
            default:
                throw new RuntimeException(sprintf(
                    'Could not execute command "%s" because operating system "%s" is not supported', $this->function_code, PHP_OS
                ));
        }
    }