func()

in go/pkg/client/cas.go [1503:1583]

• 69 lines of code
• 16 McCabe index (conditional complexity)

func (c *Client) download(data []*downloadRequest) {
	// It is possible to have multiple same files download to different locations.
	// This will download once and copy to the other locations.
	reqs := make(map[digest.Digest][]*downloadRequest)
	var metas []*ContextMetadata
	for _, r := range data {
		rs := reqs[r.digest]
		rs = append(rs, r)
		reqs[r.digest] = rs
		metas = append(metas, r.meta)
	}

	var dgs []digest.Digest

	if bool(c.useBatchOps) && bool(c.UtilizeLocality) {
		paths := make([]*TreeOutput, 0, len(data))
		for _, r := range data {
			paths = append(paths, r.output)
		}

		// This is to utilize locality in disk when writing files.
		sort.Slice(paths, func(i, j int) bool {
			return paths[i].Path < paths[j].Path
		})

		for _, path := range paths {
			dgs = append(dgs, path.Digest)
		}
	} else {
		for dg := range reqs {
			dgs = append(dgs, dg)
		}
	}

	unifiedMeta := getUnifiedMetadata(metas)
	var err error
	ctx := context.Background()
	if unifiedMeta.ActionID != "" {
		ctx, err = ContextWithMetadata(context.Background(), unifiedMeta)
	}
	if err != nil {
		afterDownload(dgs, reqs, map[digest.Digest]*MovedBytesMetadata{}, err)
		return
	}

	LogContextInfof(ctx, log.Level(2), "%d digests to download (%d reqs)", len(dgs), len(reqs))
	var batches [][]digest.Digest
	if c.useBatchOps {
		batches = c.makeBatches(ctx, dgs, !bool(c.UtilizeLocality))
	} else {
		LogContextInfof(ctx, log.Level(2), "Downloading them individually")
		for i := range dgs {
			LogContextInfof(ctx, log.Level(3), "Creating single batch of blob %s", dgs[i])
			batches = append(batches, dgs[i:i+1])
		}
	}

	for i, batch := range batches {
		i, batch := i, batch // https://golang.org/doc/faq#closures_and_goroutines
		go func() {
			if c.casDownloaders.Acquire(ctx, 1) == nil {
				defer c.casDownloaders.Release(1)
			}
			if i%logInterval == 0 {
				LogContextInfof(ctx, log.Level(2), "%d batches left to download", len(batches)-i)
			}
			if len(batch) > 1 {
				c.downloadBatch(ctx, batch, reqs)
			} else {
				rs := reqs[batch[0]]
				downloadCtx := ctx
				if len(rs) == 1 {
					// We have only one download request for this digest.
					// Download on same context as the issuing request, to support proper cancellation.
					downloadCtx = rs[0].context
				}
				c.downloadSingle(downloadCtx, batch[0], reqs)
			}
		}()
	}
}