code: def _reset() -> None:
      global _dtensor_singleton
      with _dtensor_singleton_lock:
          if _dtensor_singleton is not None:
              _dtensor_singleton.clear_tpu_core_ids()
          _dtensor_singleton = None
  
imports: import contextlib
  import threading
  from typing import Any, Callable, Optional, Sequence
  from tensorflow.dtensor.python import dtensor_device
  from tensorflow.dtensor.python import gen_dtensor_ops
  from tensorflow.dtensor.python import layout
  from tensorflow.python.eager import context
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import tensor
  from tensorflow.python.util import deprecation
  from tensorflow.python.util.tf_export import tf_export
label_desc: Use image node_id 16 for calling a global function with example usage: _reset() without return types