remove HasNext

Author: JiayiFeng

doc/design/cpp_data_feeding.md

@@ -20,9 +20,8 @@ class ReaderBase {
     PADDLE_ENFORCE(!shapes_.empty());
   }
   // Read the next batch of data. (A 'batch' can be only one instance)
+  // If the next batch doesn't exist, the 'out' will be an empty std::vector.
   virtual void ReadNext(std::vector<LoDTensor>* out) = 0;
-  // Show whether the next bacth exists.
-  virtual bool HasNext() const = 0;
 
   // Reinitialize the reader and read the file from the begin.
   virtual void ReInit() = 0;

paddle/fluid/framework/reader.h

@@ -26,7 +26,6 @@ class ReaderBase {
     PADDLE_ENFORCE(!shapes_.empty());
   }
   virtual void ReadNext(std::vector<LoDTensor>* out) = 0;
-  virtual bool HasNext() const = 0;
 
   virtual void ReInit() = 0;
 
@@ -52,8 +51,6 @@ class DecoratedReader : public ReaderBase {
     PADDLE_ENFORCE_NOT_NULL(reader_);
   }
 
-  bool HasNext() const override { return reader_->HasNext(); }
-
   void ReInit() override { reader_->ReInit(); }
 
  protected:
@@ -69,7 +66,6 @@ class ReaderHolder {
   ReaderBase* Get() const { return reader_.get(); }
 
   void ReadNext(std::vector<LoDTensor>* out) { reader_->ReadNext(out); }
-  bool HasNext() const { return reader_->HasNext(); }
   void ReInit() { reader_->ReInit(); }
 
   DDim shape(size_t idx) const { return reader_->shape(idx); }

paddle/fluid/operators/read_op.cc

@@ -60,15 +60,16 @@ class ReadOp : public framework::OperatorBase {
                const platform::Place& dev_place) const override {
     framework::ReaderHolder* reader =
         scope.FindVar(Input("Reader"))->GetMutable<framework::ReaderHolder>();
-    if (!reader->HasNext()) {
+    std::vector<std::string> out_arg_names = Outputs("Out");
+    std::vector<framework::LoDTensor> ins;
+    reader->ReadNext(&ins);
+    if (ins.empty()) {
       reader->ReInit();
+      reader->ReadNext(&ins);
       PADDLE_ENFORCE(
-          reader->HasNext(),
+          !ins.empty(),
           "Reader can not read the next data even it has been re-initialized.");
     }
-    std::vector<std::string> out_arg_names = Outputs("Out");
-    std::vector<framework::LoDTensor> ins;
-    reader->ReadNext(&ins);
     PADDLE_ENFORCE_EQ(ins.size(), out_arg_names.size());
     for (size_t i = 0; i < ins.size(); ++i) {
       auto* out =

paddle/fluid/operators/reader/create_batch_reader_op.cc

@@ -68,10 +68,10 @@ void BatchReader::ReadNext(std::vector<framework::LoDTensor>* out) {
   buffer_.clear();
   buffer_.reserve(batch_size_);
   for (int i = 0; i < batch_size_; ++i) {
-    if (reader_->HasNext()) {
-      buffer_.push_back(std::vector<framework::LoDTensor>());
-      reader_->ReadNext(&buffer_.back());
-    } else {
+    buffer_.push_back(std::vector<framework::LoDTensor>());
+    reader_->ReadNext(&buffer_.back());
+    if (buffer.back().empty()) {
+      buffer_.pop_back();
       break;
     }
   }

paddle/fluid/operators/reader/create_random_data_generator_op.cc

@@ -50,8 +50,6 @@ class RandomDataGenerator : public framework::FileReader {
     }
   }
 
-  bool HasNext() const override { return true; }
-
   void ReInit() override { return; }
 
  private:

paddle/fluid/operators/reader/create_shuffle_reader_op.cc

@@ -39,10 +39,10 @@ void ShuffleReader::ReadNext(std::vector<framework::LoDTensor>* out) {
     buffer_.clear();
     buffer_.reserve(buffer_size_);
     for (int i = 0; i < buffer_size_; ++i) {
-      if (reader_->HasNext()) {
-        buffer_.push_back(std::vector<framework::LoDTensor>());
-        reader_->ReadNext(&buffer_.back());
-      } else {
+      buffer_.push_back(std::vector<framework::LoDTensor>());
+      reader_->ReadNext(&buffer_.back());
+      if (buffer_.back().empty()) {
+        buffer_.pop_back();
         break;
       }
     }