my $v=0;
$mw->after(5000, sub { $v=1 });
$mw->waitVariable(\$v);

#!/usr/bin/perl
use strict;
use warnings 'all';
use Tk;

my $mw = tkinit;

for (0..100)
{
    my $v=0;
    $mw->after(100, sub { $v=1 });
    $mw->waitVariable(\$v);

    print "Nummer $_\n";
}

exit;

=head2 tk_sleep

=for category Tk

    $top->tk_sleep($s);

Sleep $s seconds (fractions are allowed). Use this method in Tk
programs rather than the blocking sleep function. The difference to
$top->after($s/1000) is that update events are still allowed in the
sleeping time.

=cut

sub Tk::Widget::tk_sleep {
    my($top, $s) = @_;
    my $sleep_dummy = 0;
    $top->after($s*1000,
                sub { $sleep_dummy++ });
    $top->waitVariable(\$sleep_dummy)
    unless $sleep_dummy;
}