unserialize(): Error at offset 0 of 6 bytes

            if (0 != $expire && time() > filemtime($filename) + $expire) {
                return $default;
            }
            $this->expire = $expire;
            $content      = substr($content, 32);
            if ($this->options['data_compress'] && function_exists('gzcompress')) {
                //启用数据压缩
                $content = gzuncompress($content);
            }
            $content = unserialize($content);
            return $content;
        } else {
            return $default;
        }
    }

    /**
     * 写入缓存
     * @access public