#!/usr/bin/perl --
use strict;
use warnings;
use threads;
use Thread::Queue;


my $qin  = Thread::Queue->new();
my $qout = Thread::Queue->new();

my $guithread = threads->create(
    sub {
        require MyApp::GUI; ## MyApp/GUI.pm
        MyApp::GUI::WorkQ(@_); ## uses timer to check on queue
    },
    $qin, $qout,
);

my $dbithread = threads->create(
    sub {
        require MyApp::DBFetch; ## MyApp/DBFetch.pm
        MyApp::DBFetch::WorkQ(@_);
    },
    $qin, $qout,
);

$guithread->join; ## wait for gui to finish
__END__
##</code><code>##

sub MyApp::DBFetch::WorkQ {
    my( $qin, $qout ) = @_;
    my %stash;
    while( defined( my $argRef = $qin->dequeue ) ) {
         my $action = delete $argRef->{action};
         if( $action eq 'connect' ){
             $stash{dbi} = DBI->...;
             $qout->enqueue( { status => 'you are connected' } );
         }
    }
}

##</code><code>##

sub MyApp::GUI::WorkQ {
    my( $qin, $qout ) = @_;
    ....
    Glib::Timeout->add( 50, sub { CheckQ( $qout, $statuswindow} } );
    Gtk2->main;
}

sub OnConnectButton {
    my( $qin, $passwindow ) = @_;
    my $password = $passwindow->get_text;
    ...
    $qin->enqueue( { action => 'connect', password => $password, ... } );
}

sub CheckQ {
    my( $qout, $statuswindow ) = @_;
    if( defined( my $ref = $qout->popnow ) ) {
          my $msg = $ref->{status};
          $statuswindow->set_text( $msg );
    }
    return 1; ## don't cancel timeout, repeat it
}