message: Allow MultiworkerMirroredStrategy(MWMS) use by adding checkpoint handling with temporary directories in model_lib_v2. Added missing WeakKeyDictionary cfer_fn_cache field in CollectiveAllReduceStrategyExtended.
diff: @@ -19,6 +19,7 @@ from __future__ import division
  from __future__ import print_function
  import copy
  +import weakref
  from tensorflow.core.protobuf import config_pb2
  from tensorflow.core.protobuf import rewriter_config_pb2
  @@ -173,6 +174,7 @@ class CollectiveAllReduceExtended(mirrored_strategy.MirroredExtended):
  cross_device_ops_lib.CollectiveCommunication)
  self._communication = communication
  self._initialize_strategy(self._cluster_resolver)
  + self._cfer_fn_cache = weakref.WeakKeyDictionary()
  assert isinstance(self._get_cross_device_ops(),
  cross_device_ops_lib.CollectiveAllReduce)
  