My apologies, indeed I didn't state my problem.

I have attached the code below. I would like for this simple GUI to always display the latest image file on disk, see below

For this I believe you have to loop over the mainloop.

As a simple solution I thought that I could use a timeout and call the subroutine make_gui_frame(). However, using the Timeout, I can't seem to figure out how to update what should be returned ($hbox).

If I move all the $window calls in main to the subroutine make_new_window() (see below) and then call

 
Glib::Timeout->add(1000,\&make_new_window);
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then after every Timeout call I get a new window that will always load the latest image file on disk.

So I think my issue is how to return and update $hbox so that after every Timeout I can update $window ????

#!/usr/bin/perl -w

use Glib qw/TRUE FALSE/;
use Gtk2 '-init';
use Gtk2::Gdk::Keysyms;

use threads;
use threads::shared;
#use threads::Queue;

Glib::Object->set_threadsafe (TRUE);

$window = Gtk2::Window->new('toplevel');
$window->signal_connect(delete_event => sub { Gtk2->main_quit; return 
+FALSE; });
$window->set_title("Test set up");
$window->set_border_width(0);

my $hbox=&make_gui_frame();

#### HOW DO I ACCESS $hbox using a timeout ?

Glib::Timeout->add(1000,\&make_gui_frame);

#####

$window->add($hbox);

$window->show;
Gtk2->main;

0;
        

sub make_gui_frame {

    print "LOOPING HERE \n";

## MAIN HBOX
    $hbox = Gtk2::HBox->new(FALSE, 20);
    
    my $frame = Gtk2::Frame->new('Data control');
    $frame->set_shadow_type ('out');

#method of Gtk2::Container
    $frame->set_border_width(5);

    my $box1 = Gtk2::VBox->new(FALSE, 10);
    my $box2 = Gtk2::VBox->new(FALSE, 10);
    $box2->set_border_width(10);
    $box1->pack_start($box2, TRUE, TRUE, 0);

    $button = Gtk2::Button->new("close");
    $button->signal_connect(clicked => sub { Gtk2->main_quit; });

    $box2->pack_start($button, TRUE, TRUE, 0);
    $button->can_default(TRUE);

    $frame->add($box1);

    $hbox->pack_start($frame, FALSE, FALSE,0);

    $frame = Gtk2::Frame->new('Data output and Overlay');
    $frame->set_shadow_type ('out');
#method of Gtk2::Container
    $frame->set_border_width(5);

    my $vbox_image = Gtk2::VBox->new(FALSE, 10);

#the Gtk2::Gdk::PixbufLoader is used in
# the acquisition of images in "raw" format.
#This will typically be data from a database

    
    ################################################
    ### THIS IS THE IMAGE I WANT TO HAVE LOADED 
    ################################################

    my $pixbufloader1 = Gtk2::Gdk::PixbufLoader->new;

    my $raw_data1 = `cat ../test1.jpg`;
    $pixbufloader1->write($raw_data1);

    $pixbufloader1->close;

    my $pixbuf1 = $pixbufloader1->get_pixbuf;
    my $img_orig1 = Gtk2::Image->new_from_pixbuf($pixbuf1);    

    my $pixbuf1_smaller = $pixbuf1->scale_simple(300,300,'bilinear');
    my $img1 = Gtk2::Image->new_from_pixbuf($pixbuf1_smaller);

    $vbox_image->pack_start($img1,FALSE,FALSE,0);

    $frame->add($vbox_image);

    $hbox->pack_start($frame, FALSE, FALSE,0);

    $hbox->show_all();

    return $hbox;

}

sub make_new_window {

$window = Gtk2::Window->new('toplevel');
$window->signal_connect(delete_event => sub { Gtk2->main_quit; return 
+FALSE; });
$window->set_title("Test set up");
$window->set_border_width(0);

my $hbox=&make_gui_frame();

$window->add($hbox);

$window->show;

}
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My idea, use timer, but only do this in timer

$image->clear;
$image->set_from_file( 'test.jpg' );
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where $image is a global variable