如何提升Golang字符串图片链接替换性能？

var ossclient *oss.client // oss客户端实例

func init() {
    once := sync.once{}
    once.do(func() {
        var err error
        ossclient, err = oss.new(endpoint, key, accesskeysecret)
        if err != nil {
            fmt.println("error:", err)
            os.exit(-1)
        }
    })
}

func upload(url string) string {
    type uploadresult struct {
        link string
        err  error
    }
    ch := make(chan uploadresult, 1)
    go func() {
        bucket, err := ossclient.bucket(bucketname)
        if err != nil {
            ch <- uploadresult{link: "", err: err}
            return
        }

        obj := fmt.sprintf("article/%d%d.png", time.now().unix(), *imageindex)
        *imageindex++
        err = bucket.putobject(obj, bytes.newreader(readimgdata(url)))
        if err != nil {
            ch <- uploadresult{link: "", err: err}
            return
        }

        ch <- uploadresult{link: "https://" + bucketname + "." + endpoint + "/" + obj, err: nil}
    }()

    res := <-ch
    if res.err != nil {
        fmt.println("error:", res.err)
        os.exit(-1)
    }
    return res.link
}

var linkCache map[string]string

func init() {
    linkCache = make(map[string]string)
}
func Upload(url string) string {
    if link, ok := linkCache[url]; ok {
        return link
    }

    // 其他上传代码...

    linkCache[url] = newLink
    return newLink
}