Allow exporting and loading graphs with no variables.

Change: 146257820

tensorflow/python/saved_model/builder_impl.py

@@ -336,7 +336,7 @@ class SavedModelBuilder(object):
     """
     if not self._has_saved_variables:
       raise AssertionError(
-          "Variables and assets have not been saved yet. "
+          "Graph state including variables and assets has not been saved yet. "
           "Please invoke `add_meta_graph_and_variables()` first.")
 
     # Validate the signature def map to ensure all included TensorInfos are
@@ -357,7 +357,8 @@ class SavedModelBuilder(object):
     saver = tf_saver.Saver(
         variables.global_variables(),
         sharded=True,
-        write_version=saver_pb2.SaverDef.V2)
+        write_version=saver_pb2.SaverDef.V2,
+        allow_empty=True)
 
     meta_graph_def = saver.export_meta_graph(clear_devices=clear_devices)
 
@@ -394,8 +395,9 @@ class SavedModelBuilder(object):
       main_op: Op or group of ops to execute when the graph is loaded.
     """
     if self._has_saved_variables:
-      raise AssertionError("Variables and assets have already been saved. "
-                           "Please invoke `add_meta_graph()` instead.")
+      raise AssertionError("Graph state including variables and assets has "
+                           "already been saved. Please invoke "
+                           "`add_meta_graph()` instead.")
 
     # Validate the signature def map to ensure all included TensorInfos are
     # properly populated.
@@ -426,7 +428,8 @@ class SavedModelBuilder(object):
     saver = tf_saver.Saver(
         variables.global_variables(),
         sharded=True,
-        write_version=saver_pb2.SaverDef.V2)
+        write_version=saver_pb2.SaverDef.V2,
+        allow_empty=True)
 
     # Save the variables. Also, disable writing the checkpoint state proto. The
     # file is not used during SavedModel loading. In addition, since a

tensorflow/python/saved_model/loader_impl.py

@@ -27,6 +27,7 @@ from tensorflow.core.protobuf import meta_graph_pb2
 from tensorflow.core.protobuf import saved_model_pb2
 from tensorflow.python.framework import ops
 from tensorflow.python.lib.io import file_io
+from tensorflow.python.platform import tf_logging
 from tensorflow.python.saved_model import constants
 from tensorflow.python.training import saver as tf_saver
 from tensorflow.python.util import compat
@@ -210,14 +211,18 @@ def load(sess, tags, export_dir, **saver_kwargs):
   # Build a saver by importing the meta graph def to load.
   saver = tf_saver.import_meta_graph(meta_graph_def_to_load, **saver_kwargs)
 
-  # Build the checkpoint path where the variables are located.
-  variables_path = os.path.join(
-      compat.as_bytes(export_dir),
-      compat.as_bytes(constants.VARIABLES_DIRECTORY),
-      compat.as_bytes(constants.VARIABLES_FILENAME))
+  if saver:
+    # Build the checkpoint path where the variables are located.
+    variables_path = os.path.join(
+        compat.as_bytes(export_dir),
+        compat.as_bytes(constants.VARIABLES_DIRECTORY),
+        compat.as_bytes(constants.VARIABLES_FILENAME))
 
-  # Restore the variables using the built saver in the provided session.
-  saver.restore(sess, variables_path)
+    # Restore the variables using the built saver in the provided session.
+    saver.restore(sess, variables_path)
+  else:
+    tf_logging.info("The specified SavedModel has no variables; no "
+                    "checkpoints were restored.")
 
   # Get asset tensors, if any.
   asset_tensors_dictionary = _get_asset_tensors(export_dir,

tensorflow/python/saved_model/saved_model_test.py

@@ -246,6 +246,41 @@ class SavedModelTest(test.TestCase):
       self.assertRaises(errors.NotFoundError, loader.load, sess, ["baz"],
                         export_dir)
 
+  def testGraphWithoutVariables(self):
+    export_dir = os.path.join(test.get_temp_dir(), "test_graph_has_variables")
+    builder = saved_model_builder.SavedModelBuilder(export_dir)
+
+    # Graph with no variables.
+    with self.test_session(graph=ops.Graph()) as sess:
+      constant_5_name = constant_op.constant(5.0).name
+      builder.add_meta_graph_and_variables(sess, ["foo"])
+
+    # Second graph with no variables
+    with self.test_session(graph=ops.Graph()) as sess:
+      constant_6_name = constant_op.constant(6.0).name
+      builder.add_meta_graph(["bar"])
+
+    # Save the SavedModel to disk.
+    builder.save()
+
+    # Restore the graph with tag "foo".
+    with self.test_session(graph=ops.Graph()) as sess:
+      loader.load(sess, ["foo"], export_dir)
+      # Read the constant a from the graph.
+      a = ops.get_default_graph().get_tensor_by_name(constant_5_name)
+      b = constant_op.constant(6.0)
+      c = a * b
+      self.assertEqual(30.0, sess.run(c))
+
+    # Restore the graph with tag "bar".
+    with self.test_session(graph=ops.Graph()) as sess:
+      loader.load(sess, ["bar"], export_dir)
+      # Read the constant a from the graph.
+      a = ops.get_default_graph().get_tensor_by_name(constant_6_name)
+      b = constant_op.constant(5.0)
+      c = a * b
+      self.assertEqual(30.0, sess.run(c))
+
   def testNoOverwrite(self):
     export_dir = os.path.join(test.get_temp_dir(), "test_no_overwrite")
     builder = saved_model_builder.SavedModelBuilder(export_dir)