There are a bunch of ways to do this, and using a thread has many ways of returning the data. Here is a way using a reusable thread, returning the data thru shared variables. I've included an Entry widget for you to get terminal input from.

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

# uses a reusable thread concept
# enter any value in lower entry and the sin() will be
# computed in the top entry

my $val = 0; # textvariable return variable

#create thread before any tk code is called
my $data_in:shared = '';
my $data_return:shared = '';
my $go_control:shared = 0;
my $die_control:shared = 0;

my $thr = threads->new(\&excecute);


use Tk;

my $mw = MainWindow->new();

# catch window close button to clean up threads
$mw->protocol('WM_DELETE_WINDOW' => sub { &clean_exit }); 

$mw->fontCreate('big',
   -weight=>'bold',
   -size=> 14
   );


my $label = $mw->Label(
         -bg=> 'white',
         -width => 50,
         -font => 'big',
         -textvariable => \$val )->pack();

my $txt = $mw->Entry(-bg=>'lemonchiffon', -font => 'big')->pack(qw/-fi
+ll x -pady 5/);

$mw ->bind('<Any-Enter>' => sub { $txt->Tk::focus });
$txt->bind('<Return>' => \&do_calc );
# initiate a calc whenever a return is hit in the entry widget


# you must read the shared var for the txtvar to update
# a timer to update label
my $timer = $mw->repeat(100,sub{  #every .1 second
              $val = $data_return;
            });

# a timer to initiate calculation
my $timer1 = $mw->repeat(5000,sub{  #every 5 seconds
              &do_calc             
            });

MainLoop;

sub do_calc{
   $data_in  = $txt->get() || 0; # set a default value
   #wake up thread
   $go_control = 1;
   
}

sub clean_exit{
 $timer->cancel;
 $timer1->cancel; 
  
 my @running_threads = threads->list;
 if (scalar(@running_threads) < 1){print "\nFinished\n";exit}
   else{
     $die_control = 1;
     $thr->join;
     exit;
  }
}

sub excecute{
 # thread code      
  
   while(1){
      
      if($die_control){
             print "thread finishing\n"; 
             return} 
      
      #wait for $go_control  
      if($go_control){      
          
                 if($die_control){
                    print "thread finishing\n"; 
                           return} 
               
               #do your calculation here             
               $data_return = sin( $data_in) .' '. time ;            
               print "$data_in $data_return\n";
     
               #done calculating, so turn thread back to sleep        
+     
           $go_control = 0;
        
        }else{ 

       select(undef,undef,undef,.25); }# sleep until awakened for next
+ command 
   }
    
return;
}
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