Problems with IO signal

[David Weisgerber <kx1 gmx net>]

How you described in your tutorial, you can use input_add to check for data 
on a file descriptor or socket. I did so but it won't work. Here is what I 
wrote:
$idmaster = Gtk::Gdk->input_add($socket, 'read', \&master_server, 0);

where $socket is a working network-socket of this type:
$socket = IO::Socket::INET->new(PeerAddr => $ip,
                                           PeerPort => $port,
                                           Proto => "udp")
        or error_dialog ("Fehler beim Verbinden mit dem Server");

I know that the sub master_server is never called although there are datas 
sent to $socket.

Does anybody know what I would have down wrong ???

Thx,
David Weisgerber