class_docstr: Triggers `policy_saver` save calls in a separate thread asynchronously.
class_docstr_tok: ["Triggers","`","policy_saver","`","save","calls","in","a","separate","thread","asynchronously","."]
code: def _assert_save_thread_is_alive(self):
      if self._join_save_thread or not self._save_thread.is_alive():
          raise ValueError(
              "Saving thread in AsyncPolicySaver is not alive. Either "
              "an exception has occured while saving, or the saver "
              "was closed."
          )
  
file_path: agents/tf_agents/policies/async_policy_saver.py
imports: import threading
  from typing import Text
  from absl import logging
  from tf_agents.policies import policy_saver
label_desc: Use image node_id 3 for calling the AsyncPolicySaver obj's underlying member method code with example usage: obj._assert_save_thread_is_alive() without return types