Suppose you read from that socket and do the processing in a sub.
This sub is called somewhere in the main program, probably from a menu.
You pass a reference to the MainWindow to the sub and inside the sub you call update(), like this:

. . .

my $menu = $menubar->Menubutton(qw/Name menu -tearoff 0 -text somethin
+g -underline 0 -menuitems/ =>
    [
      [command => 'read socket', -command => [\&read_socket, $MW]],
    ]
  )->pack(-side => 'left');

. . .

sub read_socket {
  my $MW = shift;

  while (some_condition) {
    do_something_with_socket;
    $MW->update();
  }
}
[download]