public synchronized void closeFileAndRemoveReader(String filePath) throws IOException {
    closedReferenceMap.remove(filePath);
    TsFileSequenceReader reader = closedFileReaderMap.remove(filePath);
    if (reader != null) {
      reader.close();
    }
    unclosedReferenceMap.remove(filePath);
    reader = unclosedFileReaderMap.remove(filePath);
    if (reader != null) {
      reader.close();
    }
  }
the key of unclosedFileReaderMap is the file path and the value of unclosedFileReaderMap is the
file's reference count.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/read/control/FileReaderManager.java