  bs->last_attempt_ai_family = AF_INET; /* so AF_INET6 is next */
…
  /* no attempt connected yet, start another one? */
  pnow = Curl_pgrs_now(data);
  if(!ongoing) {
    do_more = TRUE;
  }
  else {
    bool more_possible = cf_ai_iter_has_more(&bs->addr_iter, data);
#ifdef USE_IPV6
    if(!more_possible)
      more_possible = cf_ai_iter_has_more(&bs->ipv6_iter, data);
#endif
    do_more = more_possible &&
      (curlx_ptimediff_ms(pnow, &bs->last_attempt_started) >=
       bs->attempt_delay_ms);
    if(do_more)
      CURL_TRC_CF(data, cf, "happy eyeballs timeout expired, "
                  "start next attempt");
  }
…
  if(do_more) {
    /* start the next attempt if there is another ip address to try.
     * Alternate between address families when possible. */
    const struct Curl_addrinfo *ai = NULL;
    int ai_family = 0;
    CURL_TRC_CF(data, cf, "want to do more");
#ifdef USE_IPV6
    if((bs->last_attempt_ai_family == AF_INET) ||
       !cf_ai_iter_has_more(&bs->addr_iter, data)) {
      ai = cf_ai_iter_next(&bs->ipv6_iter, data);
      ai_family = bs->ipv6_iter.ai_family;
      CURL_TRC_CF(data, cf, "check for next AAAA address: %s",
                  ai ? "found" : "none");
    }
#endif
    if(!ai) {
      ai = cf_ai_iter_next(&bs->addr_iter, data);
      ai_family = bs->addr_iter.ai_family;
      CURL_TRC_CF(data, cf, "check for next A address: %s",
                  ai ? "found" : "none");
    }
…
      bs->last_attempt_started = *pnow;
      bs->last_attempt_ai_family = ai_family;
      /* and run everything again */

Warm-up