code: public void putAll(Map<? extends K, ? extends V> newData) {
          synchronized (this) {
              Map<K, V> newMap = new HashMap<>(internalMap);
              newMap.putAll(newData);
              internalMap = newMap;
          }
      }
docs: Inserts all the keys and values contained in the
  provided map to this map.
  
  @see java.util.Map#putAll(java.util.Map)