The while loop is blocking the eventloop. You have to use a thread or IPC of somesort to fork or thread your code. An alternative, would be to avoid the while(1) loop and sleep with a repeater. See the simple example below.

If you wanted a random timer interval, you would have to run each timer onetime only, spawning another timer as it's last action.

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

my $mw = MainWindow->new();
$mw->fontCreate('big', -size => 16 );

my $tx = $mw->Text(-bg=> 'white', -font=>'big',
                   -width => 25)->pack();

tie *STDOUT, 'Tk::Text', $tx;

$mw->repeat(1000, \&tick);

MainLoop;

my $count;

sub tick {
 ++$count;
 print "$count\n";
}
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