#!/usr/bin/perl

use warnings;
use strict;
use Tk;
use threads;

my $main = MainWindow->new();

my $th_inc = threads->new( \&kind );

sub kind {
    $main->configure(
        -title => "Hier ist der Titel"
    );
    return 0;
}
MainLoop();

Tk::Error: Can't call method "Call" on an undefined value at C:/Perl/site/lib/Tk
/After.pm line 89.
 [once,[{},after#1,idle,once,[ConfigChanged,{},{}]]]
 ("after" script)