I think the method warrants a bit more description than just its return value.

 /**
  * Get an immutable (but up-to-date) copy of the DirCache.
  * <p>
  * The returned DirCache is cached and shared with all callers
  * that used this method to obtain it.  If the on-disk file has not
  * been modified since the last request, the same instance is
  * returned to the caller.  If the on-disk file has changed, a new
  * instance is returned that contains the changes.  This allows
  * callers to treat the method return value as a stable snapshot.