Fix py_reader iterable bug (#18108)

* fix py_reader iterable bug, test=develop

* move data from buffered_reader,test=develop

paddle/fluid/operators/reader/buffered_reader.cc

@@ -14,6 +14,7 @@
 
 #include "paddle/fluid/operators/reader/buffered_reader.h"
 #include <memory>
+#include <utility>
 #include <vector>
 #include "paddle/fluid/framework/data_type.h"
 
@@ -167,7 +168,8 @@ void BufferedReader::ReadNextImpl(std::vector<framework::LoDTensor> *out) {
     return;
   }
 
-  *out = platform::is_gpu_place(place_) ? gpu_buffer_[i] : cpu_buffer_[i];
+  *out = std::move(platform::is_gpu_place(place_) ? gpu_buffer_[i]
+                                                  : cpu_buffer_[i]);
 
   // Do not push current position into ReadAsync. Push the previous position
   // Since all computation in fluid are async, change the data of

python/paddle/fluid/tests/unittests/test_decoupled_py_reader_data_check.py

@@ -0,0 +1,95 @@
+# Copyright (c) 2019 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import paddle.fluid as fluid
+import paddle
+import numpy as np
+import unittest
+import six
+
+
+class TestClass(unittest.TestCase):
+    def setUp(self):
+        self.use_double_buffer = True
+
+    def test_reader_data(self):
+        img_shape = [28, 31]
+        label_shape = [1]
+        batch_size = 32
+
+        def fake_reader():
+            for _ in six.moves.range(batch_size * 10):
+                img = np.random.random(size=img_shape).astype('float32')
+                label = np.random.random_integers(
+                    low=0, high=9, size=label_shape).astype('int64')
+                yield img, label
+
+        reader = paddle.reader.cache(fake_reader)
+        batch_reader = paddle.batch(reader, batch_size=batch_size)
+
+        places = [fluid.CPUPlace()]
+        if fluid.core.is_compiled_with_cuda():
+            places.append(fluid.CUDAPlace(0))
+
+        for p in places:
+            main_prog = fluid.Program()
+            startup_prog = fluid.Program()
+            with fluid.program_guard(main_prog, startup_prog):
+                img = fluid.layers.data(
+                    shape=img_shape, dtype='float32', name='image')
+                label = fluid.layers.data(
+                    shape=label_shape, dtype='int64', name='label')
+
+                feeder = fluid.DataFeeder(feed_list=[img, label], place=p)
+
+                use_double_buffer = self.use_double_buffer
+                if p._type() != fluid.CPUPlace()._type(
+                ) and not use_double_buffer:
+                    use_double_buffer = True
+
+                py_reader = fluid.io.PyReader(
+                    feed_list=[img, label],
+                    capacity=4,
+                    iterable=True,
+                    use_double_buffer=use_double_buffer)
+                py_reader.decorate_sample_list_generator(batch_reader, places=p)
+
+                for epoch_id in six.moves.range(10):
+                    gen = batch_reader()
+                    batch_id = 0
+                    for d in py_reader():
+                        feed = feeder.feed(next(gen))
+                        I1, L1 = feed['image'], feed['label']
+                        I2, L2 = d[0]['image'], d[0]['label']
+
+                        I1 = np.array(I1)
+                        I2 = np.array(I2)
+                        L1 = np.array(L1)
+                        L2 = np.array(L2)
+
+                        self.assertTrue(np.array_equal(I1, I2))
+                        self.assertTrue(np.array_equal(L1, L2))
+
+                        batch_id += 1
+
+                    self.assertTrue(next(gen, None) is None)
+
+
+class TestClass2(TestClass):
+    def setUp(self):
+        self.use_double_buffer = False
+
+
+if __name__ == '__main__':
+    unittest.main()