my @long_list_of_items;

# do not call this directly
sub main_process {
  if (@long_list_of_items) {
    process_item(shift @long_list_of_items);
    $button->after(50,\&main_process);
  }
}

# call this to add items to the list
sub add_item {
  my $schedule = !@long_list_of_items;
  push @long_list_of_items,@_;
  if ($schedule) {
    $button->after(50,\&main_process);
  }
}