sub _resolve {
    my ($self, $host, $request, ...) = @_;
    my $res = $self->resolver; # from Net::DNS::Resolver
...
    my $sock = $res->bgsend($host) # bgsend from Net::DNS::Resolver
        or die "No sock from bgsend";
    my $rin = '';
    vec($rin, fileno($sock), 1) = 1;
    my $nf = select($rin, undef, undef, $self->_time_remain($request)); # _time_remain is the clock for the request
    die "DNS lookup timeout" unless $nf;

    my $packet = $res->bgread($sock) # bgread from Net::DNS::Resolver
        or die "DNS bgread failure";

...