@Override public void close() throws IOException {
  if (closed.compareAndSet(false,true)) {
    close(true);
  }
}

@ Override public void close ( ) throws IOException { if ( closed . compareAndSet ( false , true ) ) { close ( true ) ; } }
closes any opened files and release any resources used by this b - tree . any pending changes will be synchronized to disk before closing . once the b - tree has been closed , it can no longer be used .
