Refine dygraph DataLoader implementation (#21634)

* refine dygraph dataloader & polish related code, test=develop

* refine code based review comment, test=develop

paddle/fluid/pybind/reader_py.cc

@@ -22,6 +22,8 @@
 #include "Python.h"
 #include "paddle/fluid/framework/ddim.h"
 #include "paddle/fluid/framework/reader.h"
+#include "paddle/fluid/imperative/layer.h"
+#include "paddle/fluid/imperative/tracer.h"
 #include "paddle/fluid/operators/reader/buffered_reader.h"
 #include "paddle/fluid/operators/reader/py_reader.h"
 #include "paddle/fluid/platform/place.h"
@@ -207,6 +209,31 @@ void BindReader(py::module *module) {
            py::call_guard<py::gil_scoped_release>())
       .def("read_next_list", &MultiDeviceFeedReader::ReadNextList,
            py::call_guard<py::gil_scoped_release>())
+      .def("read_next_var_list",
+           [](MultiDeviceFeedReader &self) {
+             auto result_list = self.ReadNextList();
+             auto &tensor_list = result_list[0];
+             std::vector<std::shared_ptr<imperative::VarBase>> var_list;
+             var_list.reserve(tensor_list.size());
+             auto func = [](framework::LoDTensor &lod_tensor) {
+               std::string act_name =
+                   imperative::GetCurrentTracer()->GenerateUniqueName(
+                       "generated_var");
+               auto new_var = std::make_shared<imperative::VarBase>(act_name);
+               new_var->SetPersistable(false);
+               new_var->SetType(framework::proto::VarType::LOD_TENSOR);
+               new_var->SetDataType(lod_tensor.type());
+               auto *tensor =
+                   new_var->MutableVar()->GetMutable<framework::LoDTensor>();
+               *tensor = std::move(lod_tensor);
+               return new_var;
+             };
+             for (auto &tensor : tensor_list) {
+               var_list.emplace_back(func(tensor));
+             }
+             return var_list;
+           },
+           py::call_guard<py::gil_scoped_release>())
       .def("reset", &MultiDeviceFeedReader::Reset,
            py::call_guard<py::gil_scoped_release>());
 

python/paddle/fluid/data_feeder.py

@@ -524,41 +524,29 @@ class NumpyToLoDTensorConverter(object):
         return t
 
 
-class ListTensorProvider(object):
-    def __init__(self, generator, places):
+class DygraphListTensorProvider(object):
+    def __init__(self, generator, place):
         self.generator = generator
         self.converters = []
-        self.places = []
-        if places:
-            if not isinstance(places, (list, tuple)):
-                places = [places]
-            assert len(
-                places) == 1, "dygraph mode CAN NOT specify multiple places."
-            for place in places:
+        if place:
             if isinstance(place, (core.CUDAPlace, core.CPUPlace)):
-                    self.places.append(place)
+                self.place = place
             else:
-                    raise ValueError(
-                        "Please specify a valid place values such as core.CPUPlace or core.CUDAPlace"
-                    )
-        if len(self.places) == 0:
-            self.places.append(_current_expected_place())
-
-    def _readData(self, iterable, places):
-        for place, each_sample in six.moves.zip(places, iterable):
-            for item in each_sample:
-                if len(self.converters) < len(item):
-                    for i in item:
+                raise ValueError("Please specify a valid place values \
+                    such as core.CPUPlace or core.CUDAPlace")
+        else:
+            self.place = _current_expected_place()
+
+    def _read_data(self, iterable, place):
+        for items in iterable:
+            if len(self.converters) < len(items):
+                for _ in items:
                     self.converters.append(NumpyToLoDTensorConverter(place))
             for each_converter, each_slot in six.moves.zip(self.converters,
-                                                               item):
+                                                           items):
                 each_converter.feed(each_slot)
         yield [c.done() for c in self.converters]
 
     def __call__(self):
-        item = []
         for batch in self.generator():
-            item.append(batch)
-            if len(item) == len(self.places):
-                yield list(self._readData(item, self.places))
-                item = []
+            yield list(self._read_data(batch, self.place))

python/paddle/fluid/reader.py

@@ -21,7 +21,7 @@ import threading
 import paddle
 from .framework import Program, Variable, program_guard, default_main_program, default_startup_program, in_dygraph_mode, cpu_places
 from .executor import global_scope
-from .data_feeder import DataFeeder, BatchedTensorProvider, ListTensorProvider
+from .data_feeder import DataFeeder, BatchedTensorProvider, DygraphListTensorProvider
 from .layers.io import monkey_patch_reader_methods, _copy_reader_var_, double_buffer
 from .unique_name import UniqueNameGenerator
 import logging
@@ -442,14 +442,13 @@ class GeneratorLoader(DataLoaderBase):
 
     def __next__(self):
         try:
-            if not in_dygraph_mode():
+            if in_dygraph_mode():
+                return self._reader.read_next_var_list()
+            else:
                 if self._return_list:
                     return self._reader.read_next_list()
                 else:
                     return self._reader.read_next()
-            else:
-                ret = self._reader.read_next_list()[0]
-                return [dygraph.base.to_variable(np.array(v)) for v in ret]
         except StopIteration:
             self._queue.close()
             self._reset()
@@ -517,7 +516,12 @@ class GeneratorLoader(DataLoaderBase):
                              drop_last=True,
                              places=None):
         assert batch_size > 0, "batch_size must be larger than 0"
-        if not in_dygraph_mode():
+        if in_dygraph_mode():
+            self.set_sample_list_generator(
+                paddle.batch(
+                    reader, batch_size=batch_size, drop_last=drop_last),
+                places=places)
+        else:
             has_lod = False
             for f in self._feed_list:
                 if f.lod_level != 0:
@@ -537,15 +541,16 @@ class GeneratorLoader(DataLoaderBase):
                     generator=reader,
                     drop_last=drop_last)
                 self.set_batch_generator(reader, places=places)
-        else:
-            self.set_sample_list_generator(
-                paddle.batch(
-                    reader, batch_size=batch_size, drop_last=drop_last),
-                places=places)
         return self
 
     def set_sample_list_generator(self, reader, places=None):
-        if not in_dygraph_mode():
+        if in_dygraph_mode():
+            provider = DygraphListTensorProvider(reader, places)
+
+            def __tensor_reader_impl__():
+                for slots in provider():
+                    yield slots[0]
+        else:
             with program_guard(Program(), Program()):
                 feeder = DataFeeder(
                     feed_list=self._feed_list, place=core.CPUPlace())
@@ -555,12 +560,6 @@ class GeneratorLoader(DataLoaderBase):
             def __tensor_reader_impl__():
                 for slots in paddle_reader():
                     yield [slots[var.name] for var in self._feed_list]
-        else:
-            provider = ListTensorProvider(reader, places)
-
-            def __tensor_reader_impl__():
-                for slots in provider():
-                    yield slots[0]
 
         self.set_batch_generator(__tensor_reader_impl__, places)
         return self
@@ -571,8 +570,8 @@ class GeneratorLoader(DataLoaderBase):
             assert places is not None, "Places cannot be None when DataLoader is iterable"
             self._places = _convert_places(places)
             if in_dygraph_mode():
-                assert len(self._places
-                           ) == 1, "Number of places must be 1 in dygraph mode"
+                assert len(self._places) == 1, \
+                    "Number of places must be 1 in dygraph mode"
         else:
             if places is not None:
                 logging.info(