class_docstr: Returns the next ps task index for placement in round-robin order.
  
  This class is not to be used directly by users.  See instead
  `replica_device_setter()` below.
docstr: Choose a ps task index for the given `Operation`.
  
  Args:
    unused_op: An `Operation` to be placed on ps.
  
  Returns:
    The next ps task index to use for the `Operation`. Returns the next
    index, in the range `[offset, offset + num_tasks)`.
code: def __call__(self, unused_op):
      """Choose a ps task index for the given `Operation`.
  
      Args:
        unused_op: An `Operation` to be placed on ps.
  
      Returns:
        The next ps task index to use for the `Operation`. Returns the next
        index, in the range `[offset, offset + num_tasks)`.
      """
      task = self._next_task
      self._next_task = (self._next_task + 1) % self._num_tasks
      return task
  
file_path: tensorflow-upstream/tensorflow/python/training/device_setter.py
imports: from tensorflow.core.framework import node_def_pb2
  from tensorflow.python.framework import device
  from tensorflow.python.platform import tf_logging
  from tensorflow.python.training import server_lib
  from tensorflow.python.util.tf_export import tf_export
label_desc: Use image node_id 2 for calling the _RoundRobinStrategy obj's underlying member method code with example usage: obj.__call__(unused_op) and returns: task