Just saw your update:

So the idea is to create a new Device::SerialPort class which inherits the original class and overrides the destructor, right?

That is the essence of the first of the two possibilities I offered. And you could go the full subclassing route if that's your thing. Personally, I wouldn't.

I'd just inject my override directly into the D::SP namespace. Ie. At the top of your program somewhere after you've used Device::SerialPort, define a subroutine:

sub Device::SerialPort::DESTROY {
    my $self = shift;
    return unless (defined $self->{NAME});
    if ($self->{"_DEBUG"}) {
        carp "Destroying $self->{NAME}";
    }
    #$self->close;
}
[download]

You'll get a "subroutine redefined" warning -- which you can disable -- but the affect will be the same as 'doing it properly' without the hassle.

Simply commenting out the #$self->close; may be enough. If not, then you will either have to investigate why not; or try my second suggestion.

Don't forget to call close() in the same thread as you created the USB connection before finishing.