use Tk;
use Tk::ProgressBar;
use strict;
use warnings;

my $count;
my $cancel;

my $mw = new MainWindow(-title => "demo");
$mw->Button(-command => sub {do_something(\$count, \$cancel)}, -text => "Do Something")->pack();
$mw->Button(-command => sub {cancel(\$cancel)}, -text => "Cancel")->pack();
my $pb = $mw->ProgressBar(
		-from => 0,
        -to => 100,
        -blocks => 100,
        -colors => [0, 'green', 50, 'yellow' , 80, 'red'],
        -variable => \$count
)->pack();
MainLoop;

sub do_something {
	my ($count_r, $cancel_r) = @_;
	$$count_r = 0;
	$$cancel_r = 0;

	while (!$$cancel_r & $$count_r < 100) {
		$$count_r ++;
		$mw->update();
		sleep(1);
	}
}

sub cancel {
	my $cancel_r = shift;
	$$cancel_r = 1;
}