docs: public List<V> values() throws InterruptedException {
          final List<V> entries = new ArrayList<>(map.size());
          for (final Entry<K, SingletonHolder<V>> ent : map.entrySet()) {
              final V entryValue = ent.getValue().get();
              if (entryValue != null) {
                  entries.add(entryValue);
              }
          }
          return entries;
      }