X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/abc241fb83523ae5ae5905ae47210f15d7e0671c..9d74b115e05fac77b49d080d9c89699b12f3c433:/sdk/go/asyncbuf/buf.go

diff --git a/sdk/go/asyncbuf/buf.go b/sdk/go/asyncbuf/buf.go
index b3b9bf221a..05af02f5f5 100644
--- a/sdk/go/asyncbuf/buf.go
+++ b/sdk/go/asyncbuf/buf.go
@@ -86,16 +86,23 @@ type reader struct {
 
 func (r *reader) Read(p []byte) (int, error) {
 	r.b.cond.L.Lock()
-	defer r.b.cond.L.Unlock()
 	for {
-		if r.b.data.Len() > r.read || len(p) == 0 {
-			n := copy(p, r.b.data.Bytes()[r.read:])
+		switch {
+		case r.read < r.b.data.Len():
+			buf := r.b.data.Bytes()
+			r.b.cond.L.Unlock()
+			n := copy(p, buf[r.read:])
 			r.read += n
 			return n, nil
+		case r.b.err != nil || len(p) == 0:
+			// r.b.err != nil means we reached EOF.  And
+			// even if we're not at EOF, there's no need
+			// to block if len(p)==0.
+			err := r.b.err
+			r.b.cond.L.Unlock()
+			return 0, err
+		default:
+			r.b.cond.Wait()
 		}
-		if r.b.err != nil {
-			return 0, r.b.err
-		}
-		r.b.cond.Wait()
 	}
 }