Merge pull request #931 from guoshengCS/fix-transformer-executor-usage

Make Transformer adapt to the latest api of ParallelExecutor

fluid/neural_machine_translation/transformer/train.py

@@ -291,11 +291,15 @@ def train(args):
         clip_last_batch=False)
 
     train_data = read_multiple(reader=train_data.batch_generator)
-
+    build_strategy = fluid.BuildStrategy()
+    # Since the token number differs among devices, customize gradient scale to
+    # use token average cost among multi-devices. and the gradient scale is
+    # `1 / token_number` for average cost.
+    build_strategy.gradient_scale_strategy = fluid.BuildStrategy.GradientScaleStrategy.Customized
     train_exe = fluid.ParallelExecutor(
         use_cuda=TrainTaskConfig.use_gpu,
         loss_name=sum_cost.name,
-        use_default_grad_scale=False)
+        build_strategy=build_strategy)
 
     def test_context():
         # Context to do validation.