protected function readConfig($filename)
    {
        if (empty($filename) || !is_string($filename) || !file_exists($filename)) {
            throw new RuntimeException(sprintf('Configuration file "%s" was not found.', $filename));
        }
        $this->_modifiedTime = max($this->_modifiedTime, filemtime($filename));

        if (function_exists('parse_ini_file')) {
            return parse_ini_file($filename, true);
        } else {
            return parse_ini_string(file_get_contents($filename), true);
        }
    }