schema: remove FileWriter's serial byte/file schema uploads after chunks are uploaded

Change-Id: I1c3a9c496ce168cc8b6d087ef1a0de99cac22127

pkg/schema/filewriter.go

@@ -181,10 +181,9 @@ func (r *noteEOFReader) Read(p []byte) (n int, err error) {
 	return
 }
 
-// br may be nil, to mean calculate it.
 func uploadString(bs blobserver.StatReceiver, br *blobref.BlobRef, s string) (*blobref.BlobRef, error) {
 	if br == nil {
-		br = blobref.SHA1FromString(s)
+		panic("nil blobref")
 	}
 	hasIt, err := serverHasBlob(bs, br)
 	if err != nil {
@@ -204,21 +203,56 @@ func uploadString(bs blobserver.StatReceiver, br *blobref.BlobRef, s string) (*b
 // "file", which is a superset of "bytes"), sets it to the provided
 // size, and populates with provided spans.  The bytes or file schema
 // blob is uploaded and its blobref is returned.
-func uploadBytes(bs blobserver.StatReceiver, bb *Builder, size int64, s []span) (*blobref.BlobRef, error) {
+func uploadBytes(bs blobserver.StatReceiver, bb *Builder, size int64, s []span) *uploadBytesFuture {
+	future := newUploadBytesFuture()
 	parts := []BytesPart{}
-	err := addBytesParts(bs, &parts, s)
-	if err != nil {
-		return nil, err
+	addBytesParts(bs, &parts, s, future)
+
+	if err := bb.PopulateParts(size, parts); err != nil {
+		future.errc <- err
+	} else {
+		json := bb.Blob().JSON()
+		br := blobref.SHA1FromString(json)
+		future.br = br
+		go func() {
+			_, err := uploadString(bs, br, json)
+			future.errc <- err
+		}()
 	}
-	err = bb.PopulateParts(size, parts)
-	if err != nil {
-		return nil, err
+	return future
+}
+
+func newUploadBytesFuture() *uploadBytesFuture {
+	return &uploadBytesFuture{
+		errc: make(chan error, 1),
 	}
-	return uploadString(bs, nil, bb.Blob().JSON())
+}
+
+// An uploadBytesFuture is an eager result of a still-in-progress uploadBytes call.
+// Call Get to wait and get its final result.
+type uploadBytesFuture struct {
+	br       *blobref.BlobRef
+	errc     chan error
+	children []*uploadBytesFuture
+}
+
+// BlobRef returns the optimistic blobref of this uploadBytes call without blocking.
+func (f *uploadBytesFuture) BlobRef() *blobref.BlobRef {
+	return f.br
+}
+
+// Get blocks for all children and returns any final error.
+func (f *uploadBytesFuture) Get() (*blobref.BlobRef, error) {
+	for _, f := range f.children {
+		if _, err := f.Get(); err != nil {
+			return nil, err
+		}
+	}
+	return f.br, <-f.errc
 }
 
 // addBytesParts uploads the provided spans to bs, appending elements to *dst.
-func addBytesParts(bs blobserver.StatReceiver, dst *[]BytesPart, spans []span) error {
+func addBytesParts(bs blobserver.StatReceiver, dst *[]BytesPart, spans []span, parent *uploadBytesFuture) {
 	for _, sp := range spans {
 		if len(sp.children) == 1 && sp.children[0].isSingleBlob() {
 			// Remove an occasional useless indirection of
@@ -237,12 +271,10 @@ func addBytesParts(bs blobserver.StatReceiver, dst *[]BytesPart, spans []span) e
 			for _, cs := range sp.children {
 				childrenSize += cs.size()
 			}
-			br, err := uploadBytes(bs, newBytes(), childrenSize, sp.children)
-			if err != nil {
-				return err
-			}
+			future := uploadBytes(bs, newBytes(), childrenSize, sp.children)
+			parent.children = append(parent.children, future)
 			*dst = append(*dst, BytesPart{
-				BytesRef: br,
+				BytesRef: future.BlobRef(),
 				Size:     uint64(childrenSize),
 			})
 		}
@@ -254,19 +286,18 @@ func addBytesParts(bs blobserver.StatReceiver, dst *[]BytesPart, spans []span) e
 			Size:    uint64(sp.to - sp.from),
 		})
 	}
-	return nil
 }
 
 // writeFileMap uploads chunks of r to bs while populating fileMap and
 // finally uploading fileMap. The returned blobref is of fileMap's
 // JSON blob. It uses rolling checksum for the chunks sizes.
-func writeFileMapRolling(bs blobserver.StatReceiver, file *Builder, r io.Reader) (outbr *blobref.BlobRef, outerr error) {
+func writeFileMapRolling(bs blobserver.StatReceiver, file *Builder, r io.Reader) (*blobref.BlobRef, error) {
 	n, spans, err := writeFileChunks(bs, file, r)
 	if err != nil {
 		return nil, err
 	}
 	// The top-level content parts
-	return uploadBytes(bs, file, n, spans)
+	return uploadBytes(bs, file, n, spans).Get()
 }
 
 // WriteFileChunks uploads chunks of r to bs while populating file.
@@ -277,8 +308,9 @@ func WriteFileChunks(bs blobserver.StatReceiver, file *Builder, r io.Reader) err
 		return err
 	}
 	parts := []BytesPart{}
-	err = addBytesParts(bs, &parts, spans)
-	if err != nil {
+	future := newUploadBytesFuture()
+	addBytesParts(bs, &parts, spans, future)
+	if _, err := future.Get(); err != nil {
 		return err
 	}
 	return file.PopulateParts(size, parts)