Add multi-thread protection and also allow atomic file creates, rename upon Close()

pkg/donut/bucket.go

@@ -318,15 +318,15 @@ func (b bucket) writeObjectMetadata(objectName string, objMetadata ObjectMetadat
 	if err != nil {
 		return iodine.New(err, nil)
 	}
-	for _, objMetadataWriter := range objMetadataWriters {
-		defer objMetadataWriter.Close()
-	}
 	for _, objMetadataWriter := range objMetadataWriters {
 		jenc := json.NewEncoder(objMetadataWriter)
 		if err := jenc.Encode(&objMetadata); err != nil {
 			return iodine.New(err, nil)
 		}
 	}
+	for _, objMetadataWriter := range objMetadataWriters {
+		objMetadataWriter.Close()
+	}
 	return nil
 }