clear out memory after reads from the dagreader

License: MIT
Signed-off-by: Jeromy <jeromyj@gmail.com>

unixfs/io/pbdagreader.go

@@ -10,7 +10,9 @@ import (
 	ft "github.com/ipfs/go-ipfs/unixfs"
 	ftpb "github.com/ipfs/go-ipfs/unixfs/pb"
 
+	node "gx/ipfs/QmNwUEK7QbwSqyKBu3mMtToo8SUc6wQJ7gdZq4gGGJqfnf/go-ipld-format"
 	proto "gx/ipfs/QmZ4Qi3GaRbjcx28Sme5eMH7RQjGkt8wHxt2a65oLaeFEV/gogo-protobuf/proto"
+	cid "gx/ipfs/QmeSrf6pzut73u6zLQkRFQ3ygt3k6XFT2kjdYP8Tnkwwyg/go-cid"
 )
 
 // DagReader provides a way to easily read the data contained in a dag.
@@ -30,6 +32,9 @@ type pbDagReader struct {
 	// NodeGetters for each of 'nodes' child links
 	promises []mdag.NodeGetter
 
+	// the cid of each child of the current node
+	links []*cid.Cid
+
 	// the index of the child link currently being read from
 	linkPosition int
 
@@ -47,30 +52,54 @@ var _ DagReader = (*pbDagReader)(nil)
 
 func NewPBFileReader(ctx context.Context, n *mdag.ProtoNode, pb *ftpb.Data, serv mdag.DAGService) *pbDagReader {
 	fctx, cancel := context.WithCancel(ctx)
-	promises := mdag.GetDAG(fctx, serv, n)
+	curLinks := getLinkCids(n)
 	return &pbDagReader{
 		node:     n,
 		serv:     serv,
 		buf:      NewBufDagReader(pb.GetData()),
-		promises: promises,
+		promises: make([]mdag.NodeGetter, len(curLinks)),
+		links:    curLinks,
 		ctx:      fctx,
 		cancel:   cancel,
 		pbdata:   pb,
 	}
 }
 
+const preloadSize = 10
+
+func (dr *pbDagReader) preloadNextNodes(ctx context.Context) {
+	beg := dr.linkPosition
+	end := beg + preloadSize
+	if end >= len(dr.links) {
+		end = len(dr.links)
+	}
+
+	for i, p := range mdag.GetNodes(ctx, dr.serv, dr.links[beg:end]) {
+		dr.promises[beg+i] = p
+	}
+}
+
 // precalcNextBuf follows the next link in line and loads it from the
 // DAGService, setting the next buffer to read from
 func (dr *pbDagReader) precalcNextBuf(ctx context.Context) error {
-	dr.buf.Close() // Just to make sure
+	if dr.buf != nil {
+		dr.buf.Close() // Just to make sure
+		dr.buf = nil
+	}
+
 	if dr.linkPosition >= len(dr.promises) {
 		return io.EOF
 	}
 
+	if dr.promises[dr.linkPosition] == nil {
+		dr.preloadNextNodes(ctx)
+	}
+
 	nxt, err := dr.promises[dr.linkPosition].Get(ctx)
 	if err != nil {
 		return err
 	}
+	dr.promises[dr.linkPosition] = nil
 	dr.linkPosition++
 
 	switch nxt := nxt.(type) {
@@ -105,6 +134,15 @@ func (dr *pbDagReader) precalcNextBuf(ctx context.Context) error {
 	}
 }
 
+func getLinkCids(n node.Node) []*cid.Cid {
+	links := n.Links()
+	out := make([]*cid.Cid, 0, len(links))
+	for _, l := range links {
+		out = append(out, l.Cid)
+	}
+	return out
+}
+
 // Size return the total length of the data from the DAG structured file.
 func (dr *pbDagReader) Size() uint64 {
 	return dr.pbdata.GetFilesize()
@@ -117,6 +155,12 @@ func (dr *pbDagReader) Read(b []byte) (int, error) {
 
 // CtxReadFull reads data from the DAG structured file
 func (dr *pbDagReader) CtxReadFull(ctx context.Context, b []byte) (int, error) {
+	if dr.buf == nil {
+		if err := dr.precalcNextBuf(ctx); err != nil {
+			return 0, err
+		}
+	}
+
 	// If no cached buffer, load one
 	total := 0
 	for {
@@ -145,6 +189,12 @@ func (dr *pbDagReader) CtxReadFull(ctx context.Context, b []byte) (int, error) {
 }
 
 func (dr *pbDagReader) WriteTo(w io.Writer) (int64, error) {
+	if dr.buf == nil {
+		if err := dr.precalcNextBuf(dr.ctx); err != nil {
+			return 0, err
+		}
+	}
+
 	// If no cached buffer, load one
 	total := int64(0)
 	for {
@@ -199,7 +249,9 @@ func (dr *pbDagReader) Seek(offset int64, whence int) (int64, error) {
 		left := offset
 		if int64(len(pb.Data)) >= offset {
 			// Close current buf to close potential child dagreader
-			dr.buf.Close()
+			if dr.buf != nil {
+				dr.buf.Close()
+			}
 			dr.buf = NewBufDagReader(pb.GetData()[offset:])
 
 			// start reading links from the beginning