#!perl -slw

use strict;
use threads;
use threads::shared;
use Thread::Queue;

## A shared var to communicate progess between work thread and TK
my $Q = new Thread::Queue;
my $pid:shared;

sub work{
	$pid = open PROC, 
    'perl -le"$|=1; print and select(undef,undef,undef,0.1) for 1 .. 1000" |'
		or die $!;
	while( <PROC> ) {
		$Q->enqueue( $_ );
	}
	close PROC;
}

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

use Tk;
use Tk::ProgressBar;

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

my $repeat;
$repeat = $mw->repeat( 100 => sub {
	while( $Q->pending ) {
		my $progress = $Q->dequeue;
		return unless $progress;
    	$repeat->cancel if $progress == 100;
    	$pb->value( $progress )
    }
} );

$mw->Button( 
	  '-text'   => 'Cancel',
	  '-command' => sub {$mw->destroy})->pack();

$mw->MainLoop;