docs: public void removeMarkedElements(boolean force) {
          long curr_time=System.nanoTime();
          for(Iterator<Map.Entry<K,Entry<V>>> it=map.entrySet().iterator(); it.hasNext();) {
              Map.Entry<K, Entry<V>> entry=it.next();
              Entry<V> tmp=entry.getValue();
              if(tmp == null)
                  continue;
              if(tmp.removable && (force || (curr_time - tmp.timestamp) >= max_age)) {
                  it.remove();
              }
          }
      }