sub select_file {
        #...;

        #$mw->Busy(-recurse => 1);  #don't recurse here
        $mw->Busy();
        
        my $file = $mw->getOpenFile(
                -title => 'select file',
                );
        $file = File::Spec->canonpath( $file );

        $mw->Unbusy(-recurse => 1);

        return $file;
}