code: public static void searchUnitMap(Consumer<Map<String, Unit>> consumer) {
          readWriteLock.readLock().lock();
          try {
              consumer.accept(Collections.unmodifiableMap(searchUnitMap));
          } finally {
              readWriteLock.readLock().unlock();
          }
      }
docs: Iterate {@link #searchUnitMap} thread-safely.
  
  @param consumer the operation for the unit map.