docs: private boolean tryToFetchElement(int index) {
          // must release read locks before acquiring write lock
          final int readLocks = stateLock.releaseReadLocksAndAcquireWriteLock();
          try {
              return couldStillTurnUp(elements[index]) ? reallyTryToFetchElement(index) : true;
          } finally {
              stateLock.downgradeWriteLockToReadLocks(readLocks);
          }
      }