Ensure serialized concrete functions are saved deterministically.

Previously, a cycle of saving and loading would randomly change which concrete
function was chosen given a set of input arguments.

PiperOrigin-RevId: 356844182
Change-Id: I5e2b3ee87866c62b619bde7b2df95d1f4f22d82c

tensorflow/python/eager/function.py

@@ -2898,8 +2898,17 @@ class FunctionCache(object):
         _FunctionGarbageCollector(self.arg_relaxed_specs)]
 
   def all_values(self):
-    """A set of all `ConcreteFunction` instances held by this cache."""
+    """A list of all `ConcreteFunction` instances held by this cache."""
-    return set(self.primary.values()) | set(self.arg_relaxed.values())
+    # We need to simultaneously make sure our returned concrete functions are
+    # unique *and* make sure they are returned in a deterministic order for
+    # serialization.
+    #
+    # TODO(b/174215821): It's likely that we ultimately would just prefer to
+    # choose the most specific concrete function shape given a set of
+    # arguments. If and when that is implemented, this logic can be revisited.
+    primary_functions = set(self.primary.values())
+    return list(self.primary.values()) + [
+        v for v in self.arg_relaxed.values() if v not in primary_functions]
 
 
 class Function(object):

tensorflow/python/saved_model/load_test.py

@@ -2169,5 +2169,32 @@ class SingleCycleTests(test.TestCase, parameterized.TestCase):
     finally:
       def_function.run_functions_eagerly(False)
 
+  def test_restored_model_concrete_function_is_deterministic(self):
+    previous_concrete_function = None
+    for _ in range(100):
+
+      class MyModel(module.Module):
+
+        @def_function.function
+        def __call__(self, x):
+          return x * constant_op.constant(3.0)
+
+      model = MyModel()
+      model(array_ops.ones((7, 3), dtype=dtypes.float32))
+      model.__call__.get_concrete_function(
+          tensor_spec.TensorSpec([None, 3], dtypes.float32))
+      loaded = cycle(model, 1)
+
+      # Ensure the newly loaded concrete function is the same as the previous
+      # after a cycle of serialization / deserialization.
+      new_concrete_function = loaded.__call__.get_concrete_function(
+          tensor_spec.TensorSpec([None, 3], dtypes.float32))
+      if previous_concrete_function is not None:
+        self.assertEqual(previous_concrete_function.pretty_printed_signature(),
+                         new_concrete_function.pretty_printed_signature())
+
+      previous_concrete_function = new_concrete_function
+
+
 if __name__ == "__main__":
   test.main()