Hi, you have been given much good advice. I just would add that this is reminscent of steganography.

I am thrown off a bit by your use of generating custom events to signal a row done. Remember, Tk should only be used for the display of the result, don't use it to do calculations. Put the calculations in a forked process or thread, and pass it back to Tk for display. It would be very responsive to a binding to the q key to stop. The Tk event loop would use a timer or a fileevent to get the resultant image data back from the thread and update the display. I probably would use GD to do the pixel manipulation, with set_pixel, in the thread or fork. Do one line at a time and return the array. Then use Tk to display the accumulated results on the canvas. Be careful with creating a new image each time you need to update the canvas, you may get a memory leak. Instead, clear out the current image object's data, and refill it.

See Re: Tk photo display: memory never released (not leaking solution feeding -data to Tk::Photo)

Here is a basic example to use threads with Tk. Re^2: Tk-with-worker-threads. Notice Tk needs a timer to read the thread data. Alternatively, you could use a fileevent to read the filhandle from the thread directly. 

#!/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 will 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
        # on win32 you may need to use IPC::Run in the thread
        my $pid = open(FH, "top -b |" ) or warn "$!\n";


        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
    }

}
#####################################################################

[download]

Good luck.

I'm not really a human, but I play one on earth. ..... an animated JAPH

In reply to Re: long computation in TK by zentara
in thread long computation in TK by BillKSmith

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