text: //   Copyright (c) 2018 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.
  
  #pragma once
  
  #include "paddle/fluid/framework/ddim.h"
  #include "paddle/fluid/framework/lod_tensor_array.h"
  #include "paddle/fluid/platform/place.h"
  
  #include <memory>
  #include <thread>
  #include <vector>
  
  namespace paddle {
  namespace framework {
  
  class ReaderBase {
   public:
    virtual void ReadNext(std::vector<LoDTensor>* out) = 0;
  
    virtual void ReInit() = 0;
  
    virtual bool HasNext() const = 0;
  
    virtual ~ReaderBase();
  };
  
  class DecoratedReader : public ReaderBase {
   public:
    explicit DecoratedReader(ReaderBase* reader) : ReaderBase(), reader_(reader) {
      PADDLE_ENFORCE_NOT_NULL(reader_);
    }
  
    void ReInit() override { reader_->ReInit(); }
  
    bool HasNext() const override { return reader_->HasNext(); }
  
   protected:
    ReaderBase* reader_;
  };
  
  class FileReader : public ReaderBase {
   public:
    explicit FileReader(const std::vector<DDim>& dims);
  
    void ReadNext(std::vector<LoDTensor>* out) override;
  
   protected:
    virtual void ReadNextImpl(std::vector<LoDTensor>* out) = 0;
  
   private:
    std::vector<DDim> dims_;
  };
  
  // The ReaderHolder is used as reader' unified wrapper,
  // making it easier to access different type reader in Variables.
  class ReaderHolder {
   public:
    void Reset(ReaderBase* reader) { reader_.reset(reader); }
  
    ReaderBase* Get() const { return reader_.get(); }
  
    void ReadNext(std::vector<LoDTensor>* out) {
      PADDLE_ENFORCE_NOT_NULL(reader_);
      reader_->ReadNext(out);
    }
    void ReInit() {
      PADDLE_ENFORCE_NOT_NULL(reader_);
      reader_->ReInit();
    }
  
    bool HasNext() const { return reader_->HasNext(); }
  
   private:
    std::unique_ptr<ReaderBase> reader_;
  };
  
  }  // namespace framework
  }  // namespace paddle
  