code: private void closeShardFiles(ShardFiles shardFiles) {
          shardFiles.deleteAllShardFiles();
          _lock.lock();
          try {
              _openShardFiles.remove(shardFiles.getKey());
              _shardFilesClosedOrExceptionCaught.signalAll();
          } finally {
              _lock.unlock();
          }
      }
docs: Cleans up any files associated with the ShardFiles instance and removes it from then open set of ShardFiles.