See Please suggest a non-forking way to do this (OS: windows) and Perl/Tk App and Interprocess Communication and How does system(1,"foo") work on Windows? for similar discussions. Here is a simple example where you can try to put your long process into it's own thread.

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

my %shash;
#share(%shash); #will work only for first level keys
my %hash;

 share ($shash{'go'});
 share ($shash{'fileno'});
 share ($shash{'pid'});
 share ($shash{'die'});
 
 $shash{'go'} = 0;
 $shash{'fileno'} = -1;
 $shash{'pid'} = -1;
 $shash{'die'} = 0;

 $hash{'thread'} = threads->new(\&work);

my $mw = MainWindow->new(-background => 'gray50');

my $text = $mw->Scrolled('Text')->pack();


my $startb = $mw->Button( -text => 'Start',
                -command=>sub{
                     $shash{'go'} = 1;
             $mw->after(100); #give pipe chance to startup
             my $fileno = $shash{'fileno'};
                     print "fileno_m $fileno\n";
          open (my $fh, "<&=$fileno") or warn "$!\n";

 # filevent works but may not work on win32, 
 # but you can use a timer instead as shown below
 $mw->fileevent(\*$fh, 'readable', );             
             while(<$fh>){
            $text->insert('end',$_);    
                $text->see('end');                  
                $mw->update;
           }

# on Win32 (untested by me) you may need 
# a timer instead of fileevent

#   my $repeater; 
#        $repeater = $mw->repeat(10,
#          sub {
#              my $bytes = sysread( "<&=$fileno", my $buf, 8192);
#          $text->insert('end',$buf);    
#                     $text->see('end');         
#          if( $shash{'go'} == 0 ){ $repeater->cancel }
#               }
#             );             
        
             }
                 )->pack();

my $stopb = $mw->Button( -text => 'Stop/Exit',
                -command=>sub{
                 $shash{'die'} = 1;
                 kill 9,$shash{'pid'};
                 $hash{'thread'}->join;         
                 exit;
              },
                 )->pack();


MainLoop;

##################################################################
sub work{
    $|++; 
    while(1){
       if($shash{'die'} == 1){ return }; 
      
       if ( $shash{'go'} == 1 ){

        #run your command here, and try to find a way to capture it's 
+output
        # into a filehandle, then use fileevent or a timer in the main
+ Tk program
        # to read the filehandle
        # on win32 you may need to use IPC::Run in the thread
        
        #use a win32 command that gives continous output
        # on linux I use top
        my $pid = open(FH, "top -b |" ) or warn "$!\n";
        #on win32 you can use system(1, $command) IIRC
        # see link above

        my $fileno = fileno(FH);
        print "fileno_t->$fileno\n";
        $shash{'fileno'} = $fileno;
        $shash{'pid'} = $pid;
       
    $shash{'go'} = 0; #turn off self before returning      
       }else
         { select(undef,undef,undef,.1) } #short sleep
    }

}
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You need to inject $mw->update; or DoOneEvent() calls into your work loop so that the window can get some CPU cycles.

Be sure to put some form of protection against clicking "go" multiple times so you don't get recursive.

Thank you all!

Putting an 'update' at the right place can do miracles.<\p>

Below is one code snippet from something I wrote many moons ago - just to demo the idea. You call something like this within your data processing loop. It is important to note that updating the GUI is an "expensive" operation and you don't want to be going crazy updating it otherwise actual work progress will grind to a snail's pace! Below I check if the percentage value has changed, if not then I return without doing a GUI operation. You will have to decide what kind of "throttle" makes sense for your application. I've got other code with an "abort" button - can't find it right now, but you can check if user has pressed that button and take appropriate action (like exit your processing loop).

When I'm finished with the progress window, I just hide it instead of destroying it. When I need it again, I just put it back on the screen.

sub update_WorkingScreen_Progress
{ 

   my $ratio = shift;             #number like .32 means 32%
   my $new_percent = int ($ratio*100); 
   
   #updating screen is expensive computationally
   #if number hasn't changed, then forget it... 
   #let 0% go through first time

   if ( ($new_percent == $percent) && ($new_percent > 0)) {return;}

   $percent = $new_percent; 
   $text = "Program is working - $extra_text...\n\n".
            "$percent percent complete\n";
   $workingScreen->update();  #this is necessary for to
                     #get the new value of $text to display!!!!!
   
}
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