sub loop_threads {

    # Threads durchlaufen
    my ( $handler_sub, $max_threads ) = @_;

    do {

        for (
            ($max_threads)
            ? threads->list(threads::joinable)
            : threads->list()
          )
        {
            &{$handler_sub}( $_->join );
        }

    } while ( $max_threads && threads->list >= $max_threads && sleep 3 );

}