public UDFClassLoader updateAndGetActiveClassLoader() throws IOException {
    UDFClassLoader deprecatedClassLoader = activeClassLoader.get();
    activeClassLoader.set(new UDFClassLoader(libRoot));
    if (deprecatedClassLoader != null) {
      deprecatedClassLoader.markAsDeprecated();
    }
    return activeClassLoader.get();
  }
activeClassLoader is used to load all classes under libRoot. libRoot may be updated before the
user executes CREATE FUNCTION or after the user executes DROP FUNCTION. Therefore, we need to
continuously maintain the activeClassLoader so that the classes it loads are always up-to-date.
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/udf/service/UDFClassLoaderManager.java