#!/usr/bin/perl
use warnings;
use strict;
use threads;
use threads::shared;

my $ret:shared = '';
my $go:shared = 0;
my $die:shared = 0;
my $val = 0;

#create thread before any tk code is called
my $thr = threads->create( \&worker );

use Tk;

my $mw = MainWindow->new();
$mw->protocol('WM_DELETE_WINDOW' => sub { &clean_exit }); 

my $canvas = $mw->Scrolled('Canvas',
              -bg =>'white',
              -scrollregion=>[0,0,1000,1000]
              )->pack(-expand=>1,-fill=>'both');

my $text;
my $button1 = $mw->Button(
         -text => 'Start',
	 -command => sub{
             $canvas->itemconfigure($text,-text=> '');
             $canvas->update;
	     $go = 1;
	  },
     )->pack();

my $button2 = $mw->Button(
         -text => 'Stop thread',
	 -command => sub{
	    $die = 1;
            $thr->join;
	  },
     )->pack();

 
my $timer = $mw->repeat(10,sub{

         if($ret ne ''){
                   $text = $canvas->createText(20,10,
                   -anchor=>'nw',
	           -fill => 'black',
	           -text => $ret,
           );
             $canvas->configure(-scrollregion => [$canvas->bbox('all')]);  
               
             $ret = '';
         }
     });

MainLoop;

sub clean_exit{
 $timer->cancel;

 my @running_threads = threads->list;
 if (scalar(@running_threads) < 1){print "\nFinished\n";exit}
   else{
     $die = 1;
     $thr->join;
     exit;
  }
}

# no Tk code in thread
sub worker {
   while(1){
       if($die){return}
         if($go){ 
          $ret = `ls -la`;
#          print "$ret\n";
          $go = 0;
        }
#   print 1;
   select(undef,undef,undef,.1);
    }
 }