Would it not be viable to do the rebuild in another directory (className.tmp) and do some file system lock/rename magic once the rebuild is finished. Hibernate search would continue to use the class name (non-temp) directory until the rebuild is completed. You'd probably need to have some lock mechanism so that searches would block while the MassIndexer renamed the directory names once the index process had finished but this should ultimately be a lock that isn't held for more than a few milliseconds.