properly release memory

fix https://github.com/chrislusf/seaweedfs/issues/301

go/storage/needle_byte_cache.go

@@ -66,7 +66,9 @@ func getBytesForFileBlock(r *os.File, offset int64, readSize int) (dataSlice []b
 }
 
 func (n *Needle) ReleaseMemory() {
-	n.rawBlock.decreaseReference()
+	if n.rawBlock != nil {
+		n.rawBlock.decreaseReference()
+	}
 }
 func ReleaseBytes(b []byte) {
 	bytesPool.Put(b)

go/storage/needle_read_write.go

@@ -144,10 +144,10 @@ func ReadNeedleBlob(r *os.File, offset int64, size uint32) (dataSlice []byte, bl
 
 func (n *Needle) ReadData(r *os.File, offset int64, size uint32, version Version) (err error) {
 	bytes, block, err := ReadNeedleBlob(r, offset, size)
-	n.rawBlock = block
 	if err != nil {
 		return err
 	}
+	n.rawBlock = block
 	n.ParseNeedleHeader(bytes)
 	if n.Size != size {
 		return fmt.Errorf("File Entry Not Found. Needle %d Memory %d", n.Size, size)

go/storage/volume.go

@@ -159,11 +159,11 @@ func (v *Volume) isFileUnchanged(n *Needle) bool {
 	if ok && nv.Offset > 0 {
 		oldNeedle := new(Needle)
 		err := oldNeedle.ReadData(v.dataFile, int64(nv.Offset)*NeedlePaddingSize, nv.Size, v.Version())
-		defer oldNeedle.ReleaseMemory()
 		if err != nil {
 			glog.V(0).Infof("Failed to check updated file %v", err)
 			return false
 		}
+		defer oldNeedle.ReleaseMemory()
 		if oldNeedle.Checksum == n.Checksum && bytes.Equal(oldNeedle.Data, n.Data) {
 			n.DataSize = oldNeedle.DataSize
 			return true
@@ -289,7 +289,6 @@ func (v *Volume) readNeedle(n *Needle) (int, error) {
 	}
 	err := n.ReadData(v.dataFile, int64(nv.Offset)*NeedlePaddingSize, nv.Size, v.Version())
 	if err != nil {
-		n.ReleaseMemory()
 		return 0, err
 	}
 	bytesRead := len(n.Data)