class_docstr: A worker manager which spawns a new thread for each worker. 
docstr: Returns true if a worker is free. 
docstr_tok: ["Returns","true","if","a","worker","is","free","."]
code: def a_worker_is_free(self):
      """Returns true if a worker is free."""
      for wid in self.worker_ids:
          if self._worker_is_free(wid):
              return self._get_last_receive_time()
      return None
  
imports: from __future__ import print_function
  from __future__ import division
  from argparse import Namespace
  from multiprocessing import Process
  import numpy
  import os
  import pickle
  import shutil
  import time
  from .exd_utils import EVAL_ERROR_CODE
label_desc: Use image node_id 11 for calling the MultiProcessingWorkerManager obj's underlying member method code with example usage: obj.a_worker_is_free() and returns: None, self