reduce v.dataFileAccessLock lock scope

weed/storage/volume_read.go

@@ -100,10 +100,11 @@ func (v *Volume) readNeedleMetaAt(n *needle.Needle, offset int64, size int32) (e
 
 // read fills in Needle content by looking up n.Id from NeedleMapper
 func (v *Volume) readNeedleDataInto(n *needle.Needle, readOption *ReadOption, writer io.Writer, offset int64, size int64) (err error) {
-	v.dataFileAccessLock.RLock()
-	defer v.dataFileAccessLock.RUnlock()
 
+	v.dataFileAccessLock.RLock()
 	nv, ok := v.nm.Get(n.Id)
+	v.dataFileAccessLock.RUnlock()
+
 	if !ok || nv.Offset.IsZero() {
 		return ErrorNotFound
 	}
@@ -120,22 +121,36 @@ func (v *Volume) readNeedleDataInto(n *needle.Needle, readOption *ReadOption, wr
 		return nil
 	}
 
-	if readOption.VolumeRevision != v.SuperBlock.CompactionRevision {
-		// the volume is compacted
-		readOption.IsOutOfRange = false
-		err = n.ReadNeedleMeta(v.DataBackend, nv.Offset.ToActualOffset(), readSize, v.Version())
-	}
-	buf := mem.Allocate(min(1024*1024, int(size)))
-	defer mem.Free(buf)
 	actualOffset := nv.Offset.ToActualOffset()
 	if readOption.IsOutOfRange {
 		actualOffset += int64(MaxPossibleVolumeSize)
 	}
 
+	buf := mem.Allocate(min(1024*1024, int(size)))
+	defer mem.Free(buf)
+
 	// read needle data
 	crc := needle.CRC(0)
 	for x := offset; x < offset+size; x += int64(len(buf)) {
+
+		v.dataFileAccessLock.RLock()
+		// possibly re-read needle offset if volume is compacted
+		if readOption.VolumeRevision != v.SuperBlock.CompactionRevision {
+			// the volume is compacted
+			readOption.IsOutOfRange = false
+			nv, ok = v.nm.Get(n.Id)
+			if !ok || nv.Offset.IsZero() {
+				v.dataFileAccessLock.RUnlock()
+				return ErrorNotFound
+			}
+			actualOffset := nv.Offset.ToActualOffset()
+			if readOption.IsOutOfRange {
+				actualOffset += int64(MaxPossibleVolumeSize)
+			}
+		}
 		count, err := n.ReadNeedleData(v.DataBackend, actualOffset, buf, x)
+		v.dataFileAccessLock.RUnlock()
+
 		toWrite := min(count, int(offset+size-x))
 		if toWrite > 0 {
 			crc = crc.Update(buf[0:toWrite])