fix compile errors

paddle/fluid/framework/reader.cc

@@ -120,11 +120,13 @@ void DoubleBufferReader::ReadNext(std::vector<LoDTensor>* out) {
   }
 
   out->clear();
-  out->resize(buffer_[read_pos_].size());
+  out->reserve(buffer_[read_pos_].size());
   // TODO(fengjiayi): This copy shall be reduced.
   for (size_t i = 0; i < buffer_[read_pos_].size(); ++i) {
-    TensorCopy(buffer_[read_pos_][i], platform::CPUPlace(), &out[i]);
-    out[i].set_lod(buffer_[read_pos_][i].lod());
+    LoDTensor dst;
+    TensorCopy(buffer_[read_pos_][i], platform::CPUPlace(), &dst);
+    dst.set_lod(buffer_[read_pos_][i].lod());
+    out->push_back(dst);
   }
 
   ++read_pos_;
@@ -134,13 +136,13 @@ void DoubleBufferReader::ReadNext(std::vector<LoDTensor>* out) {
   buffer_not_full_.notify_all();
 }
 
-bool DoubleBufferReader::HasNext() {
+bool DoubleBufferReader::HasNext() const {
   return reader_->HasNext() || !buffer_.empty();
 }
 
 void DoubleBufferReader::ProducerThreadFunc() {
   while (reader_->HasNext()) {
-    std::unique_lock<std::mutex> lck(mtx);
+    std::unique_lock<std::mutex> lck(mtx_);
     while (((write_pos_ + 1) % kDoubleBufferSize) == read_pos_) {
       buffer_not_full_.wait(lck);
     }

paddle/fluid/framework/reader.h

@@ -140,7 +140,7 @@ class BatchReader : public DecoratedReader {
 
 class DoubleBufferReader : public DecoratedReader {
  public:
-  DoubleBufferReader(ReaderBase* reader)
+  explicit DoubleBufferReader(ReaderBase* reader)
       : DecoratedReader(reader), buffer_(kDoubleBufferSize) {
     framework::Async(std::bind(&DoubleBufferReader::ProducerThreadFunc, this));
   }