code: final void cache(String hostname, E value, int ttl, EventLoop loop) {
          Entries entries = resolveCache.get(hostname);
          if (entries == null) {
              entries = new Entries(hostname);
              Entries oldEntries = resolveCache.putIfAbsent(hostname, entries);
              if (oldEntries != null) {
                  entries = oldEntries;
              }
          }
          entries.add(value, ttl, loop);
      }
docs: Cache a value for the given hostname that will automatically expire once the TTL is reached.