Method dnsEvent

src/iocore/hostdb/HostDB.cc:917–1139

DNS lookup result state

// DNS lookup result state
int
HostDBContinuation::dnsEvent(int event, HostEnt *e)
{
  if (timeout) {
    timeout->cancel(this);
    timeout = nullptr;
  }
  EThread *thread = mutex->thread_holding;
  if (event != DNS_EVENT_LOOKUP) {
    // Event should be immediate or interval.
    if (!action.continuation) {
      // Nothing to do, give up.
      if (event == EVENT_INTERVAL) {
        // Timeout - clear all queries queued up for this FQDN because none of the other ones have sent an
        // actual DNS query. If the request rate is high enough this can cause a persistent queue where the
        // DNS query is never sent and all requests timeout, even if it was a transient error.
        // See issue #8417.
        remove_and_trigger_pending_dns();
      } else {
        // "local" signal to give up, usually due this being one of those "other" queries.
        // That generally means @a this has already been removed from the queue, but just in case...
        hostDB.pending_dns_for_hash(hash.hash).remove(this);
      }
      if (hostDB.remove_from_pending_dns_for_hash(hash.hash, this)) {
        hostdb_cont_free(this);
      }
      return EVENT_DONE;
    }
    MUTEX_TRY_LOCK(lock, action.mutex, thread);
    if (!lock.is_locked()) {
      timeout = thread->schedule_in(this, HOST_DB_RETRY_PERIOD);
      return EVENT_CONT;
    }
    // [amc] Callback to client to indicate a failure due to timeout.
    // We don't try a different family here because a timeout indicates
    // a server issue that won't be fixed by asking for a different
    // address family.
    if (!action.cancelled && action.continuation) {
      action.continuation->handleEvent(EVENT_HOST_DB_LOOKUP, nullptr);
    }
    action = nullptr;
    return EVENT_DONE;
  } else {
    bool failed = !e || !e->good;

    pending_action = nullptr;

    ttl = ts_seconds(failed ? 0 : e->ttl);

    Ptr<HostDBRecord> old_r = probe(hash, false);
    // If the DNS lookup failed with NXDOMAIN, remove the old record
    if (e && e->isNameError() && old_r) {
      hostDB.refcountcache->erase(old_r->key);
      old_r = nullptr;
      Dbg(dbg_ctl_hostdb, "Removing the old record when the DNS lookup failed with NXDOMAIN");
    }

    int         valid_records = 0;