code: public void downgradeLastEdge() {
      Preconditions.checkNotNull(!endsInInode());
      Preconditions.checkState(!mEntries.isEmpty());
      Preconditions.checkState(mLockMode == LockMode.WRITE);
  
      downgradeEdge(mEntries.size() - 1);
      mLockMode = LockMode.READ;
    }
docs: Downgrades the last edge lock in the lock list from WRITE lock to READ lock.