class_docstr: Helper class for async checkpoint.
docstr: Copy the checkpointed variables from the accelerator to the host CPU.
  
  TODO(chienchunh): Get the concrete function before firstly called to avoid
                    hangining the accelerators idle during function tracing.
docstr_tok: ["Copy","the","checkpointed","variables","from","the","accelerator","to","the","host","CPU",".","TODO","(","chienchunh",")",":","Get","the","concrete","function","before","firstly","called","to","avoid","hangining","the","accelerators","idle","during","function","tracing","."]
code: def _copy_to_cpu(self):
      """Copy the checkpointed variables from the accelerator to the host CPU.
  
      TODO(chienchunh): Get the concrete function before firstly called to avoid
                        hangining the accelerators idle during function tracing.
      """
      for t in self._saveable_trackables:
          try:
              t._copy_trackable_to_cpu(
                  object_map=self._object_map
              )  # pylint: disable=protected-access
          except NotImplementedError as e:
              logging.warning("Trackable %s skipped due to: %s", t, e)
  
      for tpu_embedding in self._tpu_embedding_objects:
          tpu_embedding._retrieve_variables()
  
imports: import atexit
  import copy
  import queue
  import threading
  import time
  import weakref
  from absl import logging
  from tensorflow.python.checkpoint import checkpoint_context
  from tensorflow.python.checkpoint import trackable_view
  from tensorflow.python.distribute import device_util
  from tensorflow.python.eager import context
  from tensorflow.python.eager import def_function
  from tensorflow.python.eager import executor
  from tensorflow.python.framework import ops
  from tensorflow.python.ops import variables
  from tensorflow.python.saved_model.pywrap_saved_model import metrics
  from tensorflow.python.trackable import base
  from tensorflow.python.util import object_identity
label_desc: Use image node_id 2 for calling the AsyncCheckpointHelper obj's underlying member method code with example usage: obj._copy_to_cpu() without return types