while (!lru_list_.empty() && cache_size_ > max_bytes_) {
    RemoveBlock(block_map_.find(lru_list_.back()));
  }
}

/// Move the block to the front of the LRU list if it isn't already there.
void RamFileBlockCache::UpdateLRU(const Key& key,
                                  const std::shared_ptr<Block>& block,
                                  TF_Status* status) {
  absl::MutexLock lock(&mu_);
  if (block->timestamp == 0) {

  /// Trim the block cache to make room for another entry.
  void Trim() ABSL_EXCLUSIVE_LOCKS_REQUIRED(mu_);

  /// Update the LRU iterator for the block at `key`.
  void UpdateLRU(const Key& key, const std::shared_ptr<Block>& block,
                 TF_Status* status) ABSL_LOCKS_EXCLUDED(mu_);

  /// Remove all blocks of a file, with mu_ already held.