sub thread_do
{
    threads->self->detach();
    my $tid = threads->self->tid();
    while (1) {
        my $url = $task_q->dequeue();
        my $ua = LWP::UserAgent->new(timeout => 3);
        my $res = $ua->request(HEAD $url);
        $result_q->enqueue("$tid;$url;" . $res->code() . ";" . $res->message() . ";");
    }
}