use strict;
use Threads;
use Tk;
use Thread::Queue;
use Tk::ProgressBar;

my $comm = new Thread::Queue;
my ($mw, $percent_done)=create_gui();
threads->new(\&go, $comm, $percent_done)->detach;
$mw->repeat( 100, [\&updateScreen, $comm, $percent_done] );
MainLoop();

sub create_gui {
    my $percent_done=0;
    my $mw = MainWindow->new( -title => 'Test');
    $mw->Label( -text => "percent_done" )->pack;
    $mw->ProgressBar(-variable => \$percent_done)->pack;
    $mw->Button ( 
        -text => "Clear",
        -command => sub {$percent_done=0}
        )->pack;

    return ($mw, $percent_done);
    }
    
sub go {
    my ($comm, $percent_done)=@_;
    
    while(1) {
        $comm->enqueue( $percent_done+5);
        select undef, undef, undef, 0.1;
        }
    }

sub updateScreen {
    my ($comm, $percent_done)=@_;
    ($percent_done = $comm->dequeue ) if $comm->pending;       
    }