Modify MultipleReader

1. Removes MultipleReader's multi-thread support, for we have got
ThreadedReader.
2. Rename MultipleReader to MultiFileReader

paddle/fluid/operators/reader/create_threaded_reader_op.cc

@@ -124,7 +124,7 @@ class CreateThreadedReaderOpMaker : public DecoratedReaderMakerBase {
       can enable them by setting 'unsafe_mode' true. In this case, 
       'HasNext()' returning true only guarantees the safety of 
       invoking 'ReadNext()' in the same thread. Each thread must 
-      invoke 'HasNext()' and 'ReadNext()' in pair.
+      invoke 'HasNext()' and 'ReadNext()' in pairs.
     )DOC");
   }
 };

paddle/fluid/operators/reader/open_files_op.cc

@@ -19,25 +19,9 @@ namespace paddle {
 namespace operators {
 namespace reader {
 
-class MultipleReader : public framework::ReaderBase {
+class MultiFileReader : public framework::ReaderBase {
  public:
-  class ThreadBufferMap {
-   public:
-    std::vector<framework::LoDTensor>& operator[](
-        const std::thread::id& thread_id) {
-      std::lock_guard<std::mutex> lock(mutex_);
-      return buffer_[thread_id];
-    }
-
-    void Clear() { buffer_.clear(); }
-
-   private:
-    std::mutex mutex_;
-    std::unordered_map<std::thread::id, std::vector<framework::LoDTensor>>
-        buffer_;
-  };
-
-  MultipleReader(const std::vector<std::string>& file_names,
+  MultiFileReader(const std::vector<std::string>& file_names,
                   const std::vector<framework::DDim>& dims, size_t thread_num,
                   size_t buffer_size)
       : file_names_(file_names), dims_(dims), buffer_size_(buffer_size) {
@@ -49,7 +33,7 @@ class MultipleReader : public framework::ReaderBase {
   bool HasNext() const override;
   void ReInit() override;
 
-  ~MultipleReader() { EndScheduler(); }
+  ~MultiFileReader() { EndScheduler(); }
 
  private:
   void StartNewScheduler();
@@ -65,31 +49,27 @@ class MultipleReader : public framework::ReaderBase {
   framework::Channel<size_t>* waiting_file_idx_;
   framework::Channel<size_t>* available_thread_idx_;
   framework::Channel<std::vector<framework::LoDTensor>>* buffer_;
-  mutable ThreadBufferMap thread_buffer_map_;
 };
 
-void MultipleReader::ReadNext(std::vector<framework::LoDTensor>* out) {
+void MultiFileReader::ReadNext(std::vector<framework::LoDTensor>* out) {
   if (!HasNext()) {
     PADDLE_THROW("There is no next data!");
   }
-  auto& thread_local_buffer = thread_buffer_map_[std::this_thread::get_id()];
-  *out = thread_local_buffer;
-  thread_local_buffer.clear();
+  buffer_->Receive(out);
 }
 
-bool MultipleReader::HasNext() const {
-  auto& thread_local_buffer = thread_buffer_map_[std::this_thread::get_id()];
-  return thread_local_buffer.empty() ? buffer_->Receive(&thread_local_buffer)
-                                     : true;
+bool MultiFileReader::HasNext() const {
+  while (!buffer_->IsClosed() && !buffer_->CanReceive()) {
+  }
+  return buffer_->CanReceive();
 }
 
-void MultipleReader::ReInit() {
+void MultiFileReader::ReInit() {
   EndScheduler();
-  thread_buffer_map_.Clear();
   StartNewScheduler();
 }
 
-void MultipleReader::StartNewScheduler() {
+void MultiFileReader::StartNewScheduler() {
   size_t thread_num = prefetchers_.size();
   waiting_file_idx_ = framework::MakeChannel<size_t>(file_names_.size());
   available_thread_idx_ = framework::MakeChannel<size_t>(thread_num);
@@ -107,7 +87,7 @@ void MultipleReader::StartNewScheduler() {
   scheduler_ = std::thread([this] { ScheduleThreadFunc(); });
 }
 
-void MultipleReader::EndScheduler() {
+void MultiFileReader::EndScheduler() {
   available_thread_idx_->Close();
   buffer_->Close();
   waiting_file_idx_->Close();
@@ -119,8 +99,8 @@ void MultipleReader::EndScheduler() {
   delete waiting_file_idx_;
 }
 
-void MultipleReader::ScheduleThreadFunc() {
-  VLOG(5) << "MultipleReader schedule thread starts.";
+void MultiFileReader::ScheduleThreadFunc() {
+  VLOG(5) << "MultiFileReader schedule thread starts.";
   size_t completed_thread_num = 0;
   size_t thread_idx;
   while (available_thread_idx_->Receive(&thread_idx)) {
@@ -152,10 +132,10 @@ void MultipleReader::ScheduleThreadFunc() {
       p.join();
     }
   }
-  VLOG(5) << "MultipleReader schedule thread terminates.";
+  VLOG(5) << "MultiFileReader schedule thread terminates.";
 }
 
-void MultipleReader::PrefetchThreadFunc(std::string file_name,
+void MultiFileReader::PrefetchThreadFunc(std::string file_name,
                                          size_t thread_idx) {
   VLOG(5) << "The prefetch thread of file '" << file_name << "' starts.";
   std::unique_ptr<framework::ReaderBase> reader =
@@ -203,7 +183,7 @@ class OpenFilesOp : public framework::OperatorBase {
 
     auto* out = scope.FindVar(Output("Out"))
                     ->template GetMutable<framework::ReaderHolder>();
-    out->Reset(new MultipleReader(file_names,
+    out->Reset(new MultiFileReader(file_names,
                                    RestoreShapes(shape_concat, ranks),
                                    thread_num, buffer_size));
   }
@@ -221,7 +201,7 @@ class OpenFilesOpMaker : public FileReaderMakerBase {
     AddComment(R"DOC(
       OpenFiles Operator
 
-      An OpenFilesOp creates a MultipleReader, which is able to 
+      An OpenFilesOp creates a MultiFileReader, which is able to 
       read data multi-threaded from multiple files.
     )DOC");
   }