private function _write($file, $data, $config)
    {
        $result = file_put_contents($file, $data);
        if ($result !== false) {
            // set permissions of the new file (no execute)
            $chmod = $config->get('Cache.SerializerPermissions');
            if ($chmod !== null) {
                chmod($file, $chmod & 0666);
            }
        }
        return $result;
    }