avoid using MonitoredSession._tf_sess (#194)

tensorpack/train/base.py

@@ -20,6 +20,7 @@ from ..utils.develop import deprecated, log_deprecated
 from ..callbacks import Callback, Callbacks, MaintainStepCounter
 from ..tfutils import get_global_step_value
 from ..tfutils.modelutils import describe_model
+from ..tfutils.sesscreate import ReuseSessionCreator
 
 __all__ = ['Trainer', 'StopTraining', 'MultiPredictorTowerTrainer']
 
@@ -118,9 +119,10 @@ class Trainer(object):
         # create session
         sess_creator = self.config.session_creator
         logger.info("Finalize the graph, create the session ...")
+
+        self.sess = sess_creator.create_session()
         self._monitored_sess = tf.train.MonitoredSession(
-            session_creator=sess_creator, hooks=None)
-        self.sess = self._monitored_sess._tf_sess()  # expose the underlying session also
+            session_creator=ReuseSessionCreator(self.sess), hooks=None)
 
         # init session
         init_op = tf.global_variables_initializer()