#!perl -slw
use strict;
use threads;
use Thread::Queue;

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

sub work{
    my( $id, $delay ) = @_;
    open PROC,
    qq[ perl -le"\$|=1; print and select('','','', $delay ) for 1 .. 100" |]
        or die $!;
    while( <PROC> ) {
        $Q->enqueue( "$id:$_" );
    }
    close PROC;
}

threads->new( \&work, $_, 0.1 * $_ )->detach for 1 .. 2;

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

my $mw = MainWindow->new;
my $pb1 = $mw->ProgressBar()->pack();
my $lb  = $mw->Label( -height => 2 )->pack;
my $pb2 = $mw->ProgressBar()->pack();

my $repeat;
$repeat = $mw->repeat( 100 => sub {
    while( $Q->pending ) {
        my( $id, $progress ) = split ':', $Q->dequeue;
        return unless $progress;
        ( $id == 1 ? $pb1 : $pb2 )->value( $progress );
        if( $id == 2 && $progress == 100 ) {
            $repeat->cancel;
            $mw->exit;
        }
    }
} );


$mw->MainLoop;