Multi-threaded reader in C++

paddle/fluid/operators/reader/CMakeLists.txt

@@ -15,6 +15,7 @@ function(reader_library TARGET_NAME)
         PARENT_SCOPE)
 endfunction()
 
+reader_library(open_files_op SRCS open_files_op.cc)
 reader_library(create_random_data_generator_op SRCS create_random_data_generator_op.cc)
 reader_library(create_shuffle_reader_op SRCS create_shuffle_reader_op.cc)
 reader_library(create_batch_reader_op SRCS create_batch_reader_op.cc)

paddle/fluid/operators/reader/create_double_buffer_reader_op.cc

@@ -124,10 +124,13 @@ class CreateDoubleBufferReaderOpMaker : public DecoratedReaderMakerBase {
 };
 
 void DoubleBufferReader::ReadNext(std::vector<framework::LoDTensor>* out) {
+  if (!HasNext()) {
+    PADDLE_THROW("There is no next data!");
+  }
+
   if (local_buffer_.payloads_.empty()) {
     buffer_->Receive(&local_buffer_);
   }
-
   *out = local_buffer_.payloads_;
   local_buffer_.payloads_.clear();
   if (local_buffer_.ctx_) {

paddle/fluid/operators/reader/open_files_op.cc

@@ -0,0 +1,212 @@
+//   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.
+
+#include "paddle/fluid/framework/channel.h"
+#include "paddle/fluid/operators/reader/reader_op_registry.h"
+
+namespace paddle {
+namespace operators {
+namespace reader {
+
+class MultipleReader : public framework::ReaderBase {
+ public:
+  MultipleReader(const std::vector<std::string>& file_names,
+                 const std::vector<framework::DDim>& dims, size_t thread_num)
+      : file_names_(file_names), dims_(dims) {
+    prefetchers_.resize(thread_num);
+    StartNewScheduler();
+  }
+
+  void ReadNext(std::vector<framework::LoDTensor>* out) override;
+  bool HasNext() const override;
+  void ReInit() override;
+
+  ~MultipleReader() { EndScheduler(); }
+
+ private:
+  void StartNewScheduler();
+  void EndScheduler();
+  void ScheduleThreadFunc();
+  void PrefetchThreadFunc(std::string file_name, size_t thread_idx);
+
+  std::vector<std::string> file_names_;
+  std::vector<framework::DDim> dims_;
+  std::thread scheduler_;
+  std::vector<std::thread> prefetchers_;
+  framework::Channel<size_t>* waiting_file_idx_;
+  framework::Channel<size_t>* available_thread_idx_;
+  framework::Channel<std::vector<framework::LoDTensor>>* buffer_;
+  mutable std::vector<framework::LoDTensor> local_buffer_;
+};
+
+void MultipleReader::ReadNext(std::vector<framework::LoDTensor>* out) {
+  if (!HasNext()) {
+    PADDLE_THROW("There is no next data!");
+  }
+
+  if (local_buffer_.empty()) {
+    buffer_->Receive(&local_buffer_);
+  }
+  *out = local_buffer_;
+  local_buffer_.clear();
+}
+
+bool MultipleReader::HasNext() const {
+  return local_buffer_.empty() ? buffer_->Receive(&local_buffer_) : true;
+}
+
+void MultipleReader::ReInit() {
+  EndScheduler();
+  local_buffer_.clear();
+  StartNewScheduler();
+}
+
+void MultipleReader::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);
+  buffer_ =
+      framework::MakeChannel<std::vector<framework::LoDTensor>>(thread_num);
+
+  for (size_t i = 0; i < file_names_.size(); ++i) {
+    waiting_file_idx_->Send(&i);
+  }
+  waiting_file_idx_->Close();
+  for (size_t i = 0; i < thread_num; ++i) {
+    available_thread_idx_->Send(&i);
+  }
+
+  scheduler_ = std::thread([this] { ScheduleThreadFunc(); });
+}
+
+void MultipleReader::EndScheduler() {
+  available_thread_idx_->Close();
+  buffer_->Close();
+  waiting_file_idx_->Close();
+  if (scheduler_.joinable()) {
+    scheduler_.join();
+  }
+  delete buffer_;
+  delete available_thread_idx_;
+  delete waiting_file_idx_;
+}
+
+void MultipleReader::ScheduleThreadFunc() {
+  VLOG(5) << "MultipleReader schedule thread starts.";
+  size_t completed_thread_num = 0;
+  size_t thread_idx;
+  while (available_thread_idx_->Receive(&thread_idx)) {
+    std::thread& prefetcher = prefetchers_[thread_idx];
+    if (prefetcher.joinable()) {
+      prefetcher.join();
+    }
+    size_t file_idx;
+    if (waiting_file_idx_->Receive(&file_idx)) {
+      // Still have files to read. Start a new prefetch thread.
+      std::string file_name = file_names_[file_idx];
+      prefetcher = std::thread([this, file_name, thread_idx] {
+        PrefetchThreadFunc(file_name, thread_idx);
+      });
+    } else {
+      // No more file to read.
+      ++completed_thread_num;
+      if (completed_thread_num == prefetchers_.size()) {
+        buffer_->Close();
+        break;
+      }
+    }
+  }
+  // If users invoke ReInit() when scheduler is running, it will close the
+  // 'avaiable_thread_idx_' and prefecther threads have no way to tell scheduler
+  // to release their resource. So a check is needed before scheduler ends.
+  for (auto& p : prefetchers_) {
+    if (p.joinable()) {
+      p.join();
+    }
+  }
+  VLOG(5) << "MultipleReader schedule thread terminates.";
+}
+
+void MultipleReader::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 =
+      CreateReaderByFileName(file_name, dims_);
+  while (reader->HasNext()) {
+    std::vector<framework::LoDTensor> ins;
+    reader->ReadNext(&ins);
+    if (!buffer_->Send(&ins)) {
+      VLOG(5) << "WARNING: The buffer channel has been closed. The prefetch "
+                 "thread of file '"
+              << file_name << "' will terminate.";
+      break;
+    }
+  }
+  if (!available_thread_idx_->Send(&thread_idx)) {
+    VLOG(5) << "WARNING: The available_thread_idx_ channel has been closed. "
+               "Fail to send thread_idx.";
+  }
+  VLOG(5) << "The prefetch thread of file '" << file_name << "' terminates.";
+}
+
+class OpenFilesOp : public framework::OperatorBase {
+ public:
+  using framework::OperatorBase::OperatorBase;
+
+ private:
+  void RunImpl(const framework::Scope& scope,
+               const platform::Place& dev_place) const override {
+    const auto& shape_concat = Attr<std::vector<int>>("shape_concat");
+    const auto& ranks = Attr<std::vector<int>>("ranks");
+    PADDLE_ENFORCE(!shape_concat.empty() && !ranks.empty());
+    PADDLE_ENFORCE_EQ(std::accumulate(ranks.begin(), ranks.end(), 0),
+                      int(shape_concat.size()),
+                      "The accumulate of all ranks should be equal to the "
+                      "shape concat's length.");
+    const auto& file_names = Attr<std::vector<std::string>>("file_names");
+    PADDLE_ENFORCE(!file_names.empty(), "No file to be read!");
+    const size_t thread_num = Attr<int>("thread_num");
+
+    auto* out = scope.FindVar(Output("Out"))
+                    ->template GetMutable<framework::ReaderHolder>();
+    out->Reset(new MultipleReader(
+        file_names, RestoreShapes(shape_concat, ranks), thread_num));
+  }
+};
+
+class OpenFilesOpMaker : public FileReaderMakerBase {
+ public:
+  OpenFilesOpMaker(OpProto* op_proto, OpAttrChecker* op_checker)
+      : FileReaderMakerBase(op_proto, op_checker) {
+    AddAttr<std::vector<std::string>>("file_names", "Files to be read.");
+    AddAttr<int>("thread_num", "The maximal concurrent prefetch thread number.")
+        .GreaterThan(0);
+
+    AddComment(R"DOC(
+      OpenFiles Operator
+
+      An OpenFilesOp creates a MultipleReader, which is able to 
+      read data multi-threaded from multiple files.
+    )DOC");
+  }
+};
+
+}  // namespace reader
+}  // namespace operators
+}  // namespace paddle
+
+namespace reader = paddle::operators::reader;
+
+REGISTER_FILE_READER_OPERATOR(open_files, reader::OpenFilesOp,
+                              reader::OpenFilesOpMaker);

paddle/fluid/operators/reader/reader_op_registry.cc

@@ -36,6 +36,21 @@ std::unordered_map<std::string, FileReaderCreator>& FileReaderRegistry() {
   return regs;
 }
 
+std::unique_ptr<framework::ReaderBase> CreateReaderByFileName(
+    const std::string& file_name, const std::vector<framework::DDim>& dims) {
+  size_t separator_pos = file_name.find_last_of(kFileFormatSeparator);
+  PADDLE_ENFORCE_NE(separator_pos, std::string::npos,
+                    "File name illegal! A legal file name should be like: "
+                    "[file_name].[file_format] (e.g., 'data_file.recordio').");
+  std::string filetype = file_name.substr(separator_pos + 1);
+
+  auto itor = FileReaderRegistry().find(filetype);
+  PADDLE_ENFORCE(itor != FileReaderRegistry().end(),
+                 "No file reader registered for '%s' format.", filetype);
+  framework::ReaderBase* reader = (itor->second)(file_name, dims);
+  return std::unique_ptr<framework::ReaderBase>(reader);
+}
+
 FileReaderMakerBase::FileReaderMakerBase(
     framework::OpProtoAndCheckerMaker::OpProto* op_proto,
     framework::OpAttrChecker* op_checker)

paddle/fluid/operators/reader/reader_op_registry.h

@@ -21,6 +21,8 @@ namespace paddle {
 namespace operators {
 namespace reader {
 
+static constexpr char kFileFormatSeparator[] = ".";
+
 using FileReaderCreator = std::function<framework::ReaderBase*(
     const std::string&, const std::vector<framework::DDim>&)>;
 
@@ -29,12 +31,15 @@ std::unordered_map<std::string, FileReaderCreator>& FileReaderRegistry();
 template <typename Reader>
 int RegisterFileReader(const std::string& filetype) {
   FileReaderRegistry()[filetype] = [](
-      const std::string& fn, const std::vector<paddle::framework::DDim>& dim) {
-    return new Reader(fn, dim);
+      const std::string& fn, const std::vector<framework::DDim>& dims) {
+    return new Reader(fn, dims);
   };
   return 0;
 }
 
+std::unique_ptr<framework::ReaderBase> CreateReaderByFileName(
+    const std::string& file_name, const std::vector<framework::DDim>& dims);
+
 extern std::vector<framework::DDim> RestoreShapes(
     const std::vector<int>& shape_concat, const std::vector<int>& ranks);
 

paddle/fluid/recordio/header.cc

@@ -29,8 +29,8 @@ Header::Header(uint32_t num, uint32_t sum, Compressor c, uint32_t cs)
 
 bool Header::Parse(std::istream& is) {
   uint32_t magic;
-  size_t read_size =
-      is.readsome(reinterpret_cast<char*>(&magic), sizeof(uint32_t));
+  is.read(reinterpret_cast<char*>(&magic), sizeof(uint32_t));
+  size_t read_size = is.gcount();
   if (read_size < sizeof(uint32_t)) {
     return false;
   }

python/paddle/fluid/layers/io.py

@@ -21,7 +21,8 @@
 
 __all__ = [
     'data', 'BlockGuardServ', 'ListenAndServ', 'Send', 'open_recordio_file',
-    'read_file', 'create_shuffle_reader', 'create_double_buffer_reader'
+    'open_files', 'read_file', 'create_shuffle_reader',
+    'create_double_buffer_reader'
 ]
 
 
@@ -287,6 +288,36 @@ def open_recordio_file(filename, shapes, lod_levels, dtypes):
                              startup_var)
 
 
+def open_files(filenames, thread_num, shapes, lod_levels, dtypes):
+    dtypes = [convert_np_dtype_to_dtype_(dt) for dt in dtypes]
+    shape_concat = []
+    ranks = []
+
+    for shape in shapes:
+        shape_concat.extend(shape)
+        ranks.append(len(shape))
+
+    var_name = unique_name('multiple_reader')
+
+    startup_blk = default_startup_program().current_block()
+    startup_var = startup_blk.create_var(name=var_name)
+    startup_blk.append_op(
+        type='open_files',
+        outputs={'Out': [startup_var]},
+        attrs={
+            'shape_concat': shape_concat,
+            'lod_levels': lod_levels,
+            'ranks': ranks,
+            'file_names': filenames,
+            'thread_num': thread_num
+        })
+
+    startup_var.desc.set_dtypes(dtypes)
+    startup_var.persistable = True
+    return _copy_reader_var_(default_main_program().current_block(),
+                             startup_var)
+
+
 def __create_decorated_reader__(op_type, reader, attrs):
     var_name = unique_name(op_type)
     startup_blk = default_startup_program().current_block()

python/paddle/fluid/tests/unittests/.gitignore

@@ -1 +1,4 @@
 mnist.recordio
+mnist_0.recordio
+mnist_1.recordio
+mnist_2.recordio