#!/usr/bin/perl
use strict;
use threads qw[ async ];
use threads::shared;

our $WORKMAX ||= 1_000;

#by BrowserUk 

## A shared var to communicate progess between work thread and TK 
my $progress : shared = 0;

sub work {
    for my $item ( 0 .. $WORKMAX ) {
        { lock $progress; $progress = ( $item / $WORKMAX ) * 100; }
        select undef, undef, undef, 0.001;    ## do stuff that takes time 
    }
}

threads->new( \&work )->detach;

## For lowest memory consumption require (not use) 
## Tk::* after you've started the work thread. 
require Tk::ProgressBar;

my $mw = MainWindow->new;
my $pb = $mw->ProgressBar()->pack();

my $repeat;
$repeat = $mw->repeat(
    100 => sub {
        print $progress;
        $repeat->cancel if $progress == 100;
        $pb->value($progress);
    }
);

$mw->MainLoop;