func (p *converter) upload(bytes [][]byte) ([]string, error) {
  ch := make(chan struct{}, 4)
  wg := &sync.WaitGroup{}
  wg.Add(len(bytes))
  ret := make([]string, len(bytes))
  // 上傳
  for index, item := range bytes {
    ch <- struct{}{}
    go func(index int, imageData []byte) {
      defer func() {
        wg.Done()
        <-ch
      }()
      link, err := qiniu.UploadBinary(imageData, fmt.Sprintf("%d.png", time.Now().UnixNano()))
      if err != nil {
        log.Println("上傳圖片失敗", err.Error())
        return
      }
      ret[index] = link
    }(index, item)
  }
  wg.Wait()
  return ret, nil
}

func (p *converter) upload(bytes [][]byte) ([]string, error) {
  ret := make([]string, len(bytes))
  pool := goroutine_pool.New(4, len(bytes))

  for index, item := range bytes {
    index := index
    item := item
    pool.Submit(func() {
      link, err := qiniu.UploadBinary(item, fmt.Sprintf("%d.png", time.Now().UnixNano()))
      if err != nil {
        log.Println("上傳圖片失敗", err.Error())
        return
      }

      ret[index] = link
    })
  }
  pool.Wait()
  return ret, nil
}