Two problems , you're not passing arguments, which means you're using global variables ... argument passing is what its all about (see Re^4: Query the height of Tk::Text widget with word wrap)

The other thing is, use Thread::Queue, and then you can in one thread do only tk stuff (get data from inqueue, do stuff with it, put data on outqueue) and it the other thread you do the talking with the serial port, however many loops and blockiness and whatever you need ... (see Re: Win32::GUI window freezing, even with threading. (win32-gui-tk-thread-dequeue.pl, Thread::Queue::popnow/push))

This might help :) Re: Win32::GUI window freezing, even with threading. (win32-gui-tk-thread-dequeue.pl, Thread::Queue::popnow/push) + Re^4: Win32::GUI window freezing, even with threading. (Wrong solution), Re: Tk: Creating label in hash, Re: perl Tk thread help, Re: error on file open, Re^4: Query the height of Tk::Text widget with word wrap

Also, food for thought, tk serialport,site:perlmonks.org tk serialport -> Marrying Tk, threads and SerialPort - a COM port monitor, Re: Perl Tk and Threads

The basic idea, is to set a textvariable $input which automatically gets updated from the repeater.

use warnings;
use strict;
use Tk;
use Device::SerialPort;
 
#my $serial_port = "/dev/ttyS0";
my $serial_port = new Device::SerialPort ("/dev/ttyS0") || die "can't
open COM1\n";

#Setup Perl/Tk
my $mw = MainWindow->new();
$mw->title("Scale");

#Close button
my $button = $mw->Button(
         -text => 'Close',
         -command => sub {$mw->destroy}  # exit is better here
         )->pack(
                 -pady => 20,
                 -side => 'bottom'
         );

 my $title_label = $mw->Label(
         -text => "Weigh-Tronix"
         )->pack(
                 -side => 'left');

 my $input = '---------------';
 my $display_label = $mw->Label(
         -textvariable => \$input,
         -width=>15,  #keep the width stable at 15
                    )->pack(
          -side => 'left');

 # every 10 millisecs update from port
 $mw->repeat(10, sub{
       # $input = $port->input;
       #or maybe better
       if(defined $port->input){ $input = $port->input  }

 });

MainLoop;
 __END__
[download]

Thank you, eventually i managed to set up the 'serial' thread and i can share its '@values' with Tk but the problem is that it's still in an infinite while loop.

$mw->repeat(1000,sub{
            print "@values"."\n";           
             });
[download]

But is it possible to run a thread when i want it to run not just in a while(1) loop all the time?

I tried to pass another variable to my serial thread which determines the running state

share @values;
share $opened_port;
[download]

Where $opened_port is set when i click on the Open button

sub opening_port
{
require Win32::SerialPort;
$serial=Win32::SerialPort->new("COM6");
$serial->baudrate(9600)        || die "Bad baudrate";
        $serial->parity('none')        || die "Bad parity";
        $serial->databits(8)        || die "Bad databits";
        $serial->stopbits(1)        || die "Bad stopbits";
        #$serial->buffers(4096,4096)    || die "Buffer error";
        $serial->handshake("none")    || die "Bad handshake method";
        $serial->write_settings;
        

while(1)
{
print $opened_port;
if($opened_port) {
   my @array;
   my $string;
   my $i=0;
   do 
   {
   $string=$serial->read(1);                    #Beolvass egy karakter
+et a sorosportról
   if((ord($string) >= 0x09 && ord($string) <=0x7A) || $string eq '\t'
+ || $string eq '\n') #megvizsgálja, hogy a beolvasott karakter megfel
+el-e az ASCII kritériumoknak
   {
   $array[$i]=$string; #elmenti a tömbbe i.-ik helyére az adott karakt
+ert
   $i++; #növeli az index értékét
   } 
   }while($string ne "\n" ); #addig fut a program amíg nem \n a beolva
+sott karakter
   $i=0;
$string = join('' , @array ) ;      #ezután egy skalárba összef&#369;z
+i a tömb elemeit, egymás után - nincs szeparátor
chomp($string); # leszedi a \r és \n karaktereket a string végér&#337;
+l
@values = split('\t',$string);       #majd felbontja a skalárt a tabul
+árotok mentén
# az 1-es index tartalmazza a a h&#337;mérsékleti adatokat, a 3-as ind
+ex az id&#337;t
}    
}
}
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Of course i get an error which says that $opened_port is uninitialized, so i guess that shareing variable is a child to parent thing and it won't work in the other way. But what could be the proper way to read the serial port on button press and close it on another button event?

Okay I was a noob and shared a wrong variable with the serial thread...Now everything works like a charm!! Thank you Anonymous Monk and zentara for helping me!

One more question :) Is there a way to share my $serial object with the serialport thread?

I want to share this:

$serial=(Win32::SerialPort->new($ports[$portname])

So my serial worker thread could read from this. The only need for that is cause i select COMx ports from a listbox and i don't know how to tell the thread to read from the specific port

my $serial :shared = shared_clone({});
bless($serial, 'Serial');
[download]

When i share my serial object i get an error at $serial->read(1); line saying "Thread 1 terminated abnormally: Can't call method "read" on an undefined value"