#!/usr/bin/perl

use Gtk2 '-init';
use Glib qw/TRUE FALSE/;
use threads;
use threads::shared;
use DBI;
use DBD::mysql;

our $type="mysql";
our $database="username";
our $host="http://mysite.com";
our $port="3306";
our $tablename="login";
our $user="username";
our $pwd="************";

our $dsn="dbi:$type:$database:$host:$port";
our $query;
our $queryhandle;
my $str:shared=0;

my $window=Gtk2::Window->new;
$window->signal_connect('delete_event',sub{Gtk2->main_quit;});
$window->set_title("Perl Gtk2 Tutorial");

my $vbox=Gtk2::VBox->new;
my $label=Gtk2::Label->new("Username: ");
my $button=Gtk2::Button->new("Check");
my $entry=Gtk2::Entry->new();
$button->signal_connect(clicked=>sub{
	$str=$entry->get_text;
	my $thr=threads->create(\&continue_checking);
});
$vbox->add($label);
$vbox->add($entry);
$vbox->add($button);
$window->add($vbox);
$window->show_all;
Gtk2->main;
sub continue_checking{
	our $connect=DBI->connect($dsn,$user,$pwd)or die &mysql_Err;
	$query="SELECT username FROM login WHERE username=\"$str\"";
	$queryhandle=$connect->prepare($query);
	$queryhandle->execute;
	$queryhandle->bind_columns(undef, \my $user_name);
	while ($queryhandle->fetch()) {
		if("$str" eq "$user_name"){
			&main;
		}
	}	
}
sub main{
	my $mw=Gtk2::Window->new;
	$mw->set_default_size(250, 250);
	my $label=Gtk2::Label->new("username $str is already exist");
	$mw->add($label);
	$mw->show_all;
	$mw->show;
}
->Error Result<-
GLib-GObject-WARNING **: cannot register existing type `GConnectFlags' at /usr/lib/perl/5.14/DynaLoader.pm line 207.
Pango-WARNING **: shaping failure, expect ugly output. shape-engine='BasicEngineFc', font='DejaVu Sans 9.9990234375', text='' at server.pl line 40.
Segmentation fault