class_docstr: Step a single env in a separate process for lock free paralellism.
class_docstr_tok: ["Step","a","single","env","in","a","separate","process","for","lock","free","paralellism","."]
docstr: Wait for a message from the worker process and return its payload.
  
  Raises:
    Exception: An exception was raised inside the worker process.
    KeyError: The reveived message is of an unknown type.
  
  Returns:
    Payload object of the message.
docstr_tok: ["Wait","for","a","message","from","the","worker","process","and","return","its","payload",".","Raises",":","Exception",":","An","exception","was","raised","inside","the","worker","process",".","KeyError",":","The","reveived","message","is","of","an","unknown","type",".","Returns",":","Payload","object","of","the","message","."]
code: def _receive(self):
      """Wait for a message from the worker process and return its payload.
  
      Raises:
        Exception: An exception was raised inside the worker process.
        KeyError: The reveived message is of an unknown type.
  
      Returns:
        Payload object of the message.
      """
      message, payload = self._conn.recv()
      # Re-raise exceptions in the main process.
      if message == self._EXCEPTION:
          stacktrace = payload
          raise Exception(stacktrace)
      if message == self._RESULT:
          return payload
      self.close()
      raise KeyError(
          "Received message of unexpected type {}".format(message)
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import atexit
  import sys
  import traceback
  from typing import Any, Callable, Sequence, Text, Union
  from absl import logging
  import cloudpickle
  import gin
  import numpy
  import tensorflow
  from tf_agents.environments import py_environment
  from tf_agents.system import system_multiprocessing
  from tf_agents.trajectories import time_step
  from tf_agents.typing import types
  from tf_agents.utils import nest_utils
label_desc: Use image node_id 14 for calling the ProcessPyEnvironment obj's underlying member method code with example usage: obj._receive() and returns: payload