From 1a25f3cd07dd52e50e52d6071fa5aa32b531db12 Mon Sep 17 00:00:00 2001
From: fengjiayi <fengjiayi@baidu.com>
Date: Wed, 25 Apr 2018 19:32:08 +0800
Subject: [PATCH 1/7] Add reader blocking queue

---
 paddle/fluid/operators/reader/CMakeLists.txt  |   2 +
 .../fluid/operators/reader/blocking_queue.h   | 117 +++++++++
 .../reader/reader_blocking_queue_test.cc      | 224 ++++++++++++++++++
 3 files changed, 343 insertions(+)
 create mode 100644 paddle/fluid/operators/reader/blocking_queue.h
 create mode 100644 paddle/fluid/operators/reader/reader_blocking_queue_test.cc

diff --git a/paddle/fluid/operators/reader/CMakeLists.txt b/paddle/fluid/operators/reader/CMakeLists.txt
index 845528860f..3106978eb0 100644
--- a/paddle/fluid/operators/reader/CMakeLists.txt
+++ b/paddle/fluid/operators/reader/CMakeLists.txt
@@ -23,5 +23,7 @@ reader_library(create_recordio_file_reader_op SRCS create_recordio_file_reader_o
 reader_library(create_double_buffer_reader_op SRCS create_double_buffer_reader_op.cc)
 reader_library(create_multi_pass_reader_op SRCS create_multi_pass_reader_op.cc)
 reader_library(create_threaded_reader_op SRCS create_threaded_reader_op.cc)
+
+cc_test(reader_blocking_queue_test SRCS reader_blocking_queue_test.cc)
 # Export local libraries to parent
 set(READER_LIBRARY ${LOCAL_READER_LIBS} PARENT_SCOPE)
diff --git a/paddle/fluid/operators/reader/blocking_queue.h b/paddle/fluid/operators/reader/blocking_queue.h
new file mode 100644
index 0000000000..4a54ccd5e8
--- /dev/null
+++ b/paddle/fluid/operators/reader/blocking_queue.h
@@ -0,0 +1,117 @@
+//   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 <algorithm>
+#include <condition_variable>  // NOLINT
+#include <deque>
+#include <memory>
+
+#include "paddle/fluid/platform/enforce.h"
+
+namespace paddle {
+namespace operators {
+namespace reader {
+
+template <typename T>
+class BlockingQueue {
+ public:
+  explicit BlockingQueue(size_t capacity)
+      : capacity_(capacity), closed_(false) {
+    PADDLE_ENFORCE_GT(
+        capacity_, 0,
+        "The capacity of a reader::BlockingQueue must be greater than 0.");
+  }
+
+  bool Send(const T& elem) {
+    std::unique_lock<std::mutex> lock(mutex_);
+    send_cv_.wait(lock, [&] { return queue_.size() < capacity_ || closed_; });
+    if (closed_) {
+      return false;
+    } else {
+      PADDLE_ENFORCE_LT(queue_.size(), capacity_);
+      queue_.push_back(elem);
+      receive_cv_.notify_one();
+      return true;
+    }
+  }
+
+  bool Send(T&& elem) {
+    std::unique_lock<std::mutex> lock(mutex_);
+    send_cv_.wait(lock, [&] { return queue_.size() < capacity_ || closed_; });
+    if (closed_) {
+      return false;
+    } else {
+      PADDLE_ENFORCE_LT(queue_.size(), capacity_);
+      queue_.emplace_back(std::move(elem));
+      receive_cv_.notify_one();
+      return true;
+    }
+  }
+
+  bool Receive(T* elem) {
+    std::unique_lock<std::mutex> lock(mutex_);
+    receive_cv_.wait(lock, [&] { return !queue_.empty() || closed_; });
+    if (!queue_.empty()) {
+      PADDLE_ENFORCE_NOT_NULL(elem);
+      *elem = queue_.front();
+      queue_.pop_front();
+      send_cv_.notify_one();
+      return true;
+    } else {
+      PADDLE_ENFORCE(closed_);
+      return false;
+    }
+  }
+
+  void Close() {
+    std::lock_guard<std::mutex> lock(mutex_);
+    closed_ = true;
+    send_cv_.notify_all();
+    receive_cv_.notify_all();
+  }
+
+  bool IsClosed() {
+    std::lock_guard<std::mutex> lock(mutex_);
+    return closed_;
+  }
+
+  bool CanSend() {
+    std::lock_guard<std::mutex> lock(mutex_);
+    return !closed_ && queue_.size() < capacity_;
+  }
+
+  bool CanReceive() {
+    std::lock_guard<std::mutex> lock(mutex_);
+    return !queue_.empty();
+  }
+
+  size_t Cap() {
+    std::lock_guard<std::mutex> lock(mutex_);
+    return capacity_;
+  }
+
+ private:
+  size_t capacity_;
+  bool closed_;
+  std::deque<T> queue_;
+
+  std::mutex mutex_;
+  std::condition_variable receive_cv_;
+  std::condition_variable send_cv_;
+};
+}  // namespace reader
+}  // namespace operators
+}  // namespace paddle
diff --git a/paddle/fluid/operators/reader/reader_blocking_queue_test.cc b/paddle/fluid/operators/reader/reader_blocking_queue_test.cc
new file mode 100644
index 0000000000..07c22fe2bf
--- /dev/null
+++ b/paddle/fluid/operators/reader/reader_blocking_queue_test.cc
@@ -0,0 +1,224 @@
+//   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 <chrono>  // NOLINT
+#include <set>
+#include <thread>  // NOLINT
+#include <vector>
+#include "gtest/gtest.h"
+
+#include "paddle/fluid/operators/reader/blocking_queue.h"
+
+using paddle::operators::reader::BlockingQueue;
+
+TEST(BlockingQueue, CapacityTest) {
+  size_t cap = 10;
+  BlockingQueue<int> q(cap);
+  EXPECT_EQ(q.Cap(), cap);
+}
+
+TEST(BlockingQueue, CanSendTest) {
+  size_t cap = 1;
+  BlockingQueue<int> q(cap);
+  q.Send(1);
+  EXPECT_FALSE(q.CanSend());
+}
+
+void FirstInFirstOut(size_t queue_cap, size_t elem_num, size_t send_time_gap,
+                     size_t receive_time_gap) {
+  BlockingQueue<size_t> q(queue_cap);
+  std::thread sender([&]() {
+    for (size_t i = 0; i < elem_num; ++i) {
+      std::this_thread::sleep_for(std::chrono::milliseconds(send_time_gap));
+      EXPECT_TRUE(q.Send(i));
+    }
+    q.Close();
+  });
+  size_t count = 0;
+  while (true) {
+    std::this_thread::sleep_for(std::chrono::milliseconds(receive_time_gap));
+    size_t elem;
+    if (!q.Receive(&elem)) {
+      break;
+    }
+    EXPECT_EQ(elem, count++);
+  }
+  sender.join();
+  EXPECT_EQ(count, elem_num);
+  EXPECT_TRUE(q.IsClosed());
+}
+
+TEST(BlockingQueue, FirstInFirstOutTest) {
+  FirstInFirstOut(2, 5, 2, 50);
+  FirstInFirstOut(2, 5, 50, 2);
+  FirstInFirstOut(10, 3, 50, 2);
+  FirstInFirstOut(10, 3, 2, 50);
+}
+
+TEST(BlockingQueue, SenderBlockingTest) {
+  const size_t queue_cap = 2;
+  BlockingQueue<size_t> q(queue_cap);
+  size_t send_count = 0;
+  std::thread sender([&]() {
+    for (size_t i = 0; i < 5; ++i) {
+      if (!q.Send(i)) {
+        break;
+      }
+      ++send_count;
+    }
+  });
+  std::this_thread::sleep_for(std::chrono::milliseconds(200));
+  q.Close();
+  sender.join();
+  EXPECT_EQ(send_count, queue_cap);
+  std::vector<size_t> res;
+  while (q.CanReceive()) {
+    size_t elem;
+    EXPECT_TRUE(q.Receive(&elem));
+    res.push_back(elem);
+  }
+  EXPECT_EQ(res.size(), queue_cap);
+  for (size_t i = 0; i < res.size(); ++i) {
+    EXPECT_EQ(res[i], i);
+  }
+}
+
+TEST(BlockingQueue, ReceiverBlockingTest) {
+  const size_t queue_cap = 5;
+  BlockingQueue<size_t> q(queue_cap);
+  std::vector<size_t> receive_res;
+  std::thread receiver([&]() {
+    size_t elem;
+    while (true) {
+      if (!q.Receive(&elem)) {
+        break;
+      }
+      receive_res.push_back(elem);
+    }
+  });
+  std::vector<size_t> to_send{2, 1, 7};
+  for (auto e : to_send) {
+    q.Send(e);
+  }
+  q.Close();
+  receiver.join();
+  EXPECT_EQ(receive_res.size(), to_send.size());
+  for (size_t i = 0; i < to_send.size(); ++i) {
+    EXPECT_EQ(receive_res[i], to_send[i]);
+  }
+}
+
+void CheckIsUnorderedSame(const std::vector<std::vector<size_t>>& v1,
+                          const std::vector<std::vector<size_t>>& v2) {
+  std::set<size_t> s1;
+  std::set<size_t> s2;
+  for (auto vec : v1) {
+    for (size_t elem : vec) {
+      s1.insert(elem);
+    }
+  }
+  for (auto vec : v2) {
+    for (size_t elem : vec) {
+      s2.insert(elem);
+    }
+  }
+  EXPECT_EQ(s1.size(), s2.size());
+  auto it1 = s1.begin();
+  auto it2 = s2.begin();
+  while (it1 != s1.end()) {
+    EXPECT_EQ(*it1, *it2);
+    ++it1;
+    ++it2;
+  }
+}
+
+void MultiSenderMultiReceiver(const size_t queue_cap,
+                              const std::vector<std::vector<size_t>>& to_send,
+                              size_t receiver_num, size_t send_time_gap,
+                              size_t receive_time_gap) {
+  BlockingQueue<size_t> q(queue_cap);
+  size_t sender_num = to_send.size();
+  std::vector<std::thread> senders;
+  for (size_t s_idx = 0; s_idx < sender_num; ++s_idx) {
+    senders.emplace_back(std::thread([&, s_idx] {
+      for (size_t elem : to_send[s_idx]) {
+        std::this_thread::sleep_for(std::chrono::milliseconds(send_time_gap));
+        EXPECT_TRUE(q.Send(elem));
+      }
+    }));
+  }
+  std::vector<std::thread> receivers;
+  std::mutex mu;
+  std::vector<std::vector<size_t>> res;
+  for (size_t r_idx = 0; r_idx < receiver_num; ++r_idx) {
+    receivers.emplace_back(std::thread([&] {
+      std::vector<size_t> receiver_res;
+      while (true) {
+        std::this_thread::sleep_for(
+            std::chrono::milliseconds(receive_time_gap));
+        size_t elem;
+        if (!q.Receive(&elem)) {
+          break;
+        }
+        receiver_res.push_back(elem);
+      }
+      std::lock_guard<std::mutex> lock(mu);
+      res.push_back(receiver_res);
+    }));
+  }
+  for (auto& t : senders) {
+    t.join();
+  }
+  q.Close();
+  for (auto& t : receivers) {
+    t.join();
+  }
+  CheckIsUnorderedSame(to_send, res);
+}
+
+TEST(BlockingQueue, MultiSenderMultiReaderTest) {
+  std::vector<std::vector<size_t>> to_send_1{{2, 3, 4}, {9}, {0, 7, 15, 6}};
+  MultiSenderMultiReceiver(2, to_send_1, 2, 0, 0);
+  MultiSenderMultiReceiver(10, to_send_1, 2, 0, 0);
+  MultiSenderMultiReceiver(2, to_send_1, 20, 0, 0);
+  MultiSenderMultiReceiver(2, to_send_1, 2, 50, 0);
+  MultiSenderMultiReceiver(2, to_send_1, 2, 0, 50);
+
+  std::vector<std::vector<size_t>> to_send_2{
+      {2, 3, 4}, {}, {0, 7, 15, 6, 9, 32}};
+  MultiSenderMultiReceiver(2, to_send_2, 3, 0, 0);
+  MultiSenderMultiReceiver(20, to_send_2, 3, 0, 0);
+  MultiSenderMultiReceiver(2, to_send_2, 30, 0, 0);
+  MultiSenderMultiReceiver(2, to_send_2, 3, 50, 0);
+  MultiSenderMultiReceiver(2, to_send_2, 3, 0, 50);
+}
+
+struct MyClass {
+  MyClass() : val_(0) {}
+  explicit MyClass(int val) : val_(val) {}
+  MyClass(const MyClass& b) { val_ = b.val_; }
+  MyClass(MyClass&& b) { val_ = b.val_; }
+  void operator=(const MyClass& b) { val_ = b.val_; }
+
+  int val_;
+};
+
+TEST(BlockingQueue, MyClassTest) {
+  BlockingQueue<MyClass> q(2);
+  MyClass a(200);
+  q.Send(std::move(a));
+  MyClass b;
+  q.Receive(&b);
+  EXPECT_EQ(a.val_, b.val_);
+}

From a7866113146229514870f51c5c7d2c6001eada60 Mon Sep 17 00:00:00 2001
From: fengjiayi <fengjiayi@baidu.com>
Date: Wed, 25 Apr 2018 19:41:52 +0800
Subject: [PATCH 2/7] Replace Channel in MultiFileReader with BlockingQueue

---
 .../fluid/operators/reader/open_files_op.cc   | 26 +++++++++----------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/paddle/fluid/operators/reader/open_files_op.cc b/paddle/fluid/operators/reader/open_files_op.cc
index 779dc8a6a0..461b56c7a4 100644
--- a/paddle/fluid/operators/reader/open_files_op.cc
+++ b/paddle/fluid/operators/reader/open_files_op.cc
@@ -14,7 +14,7 @@
 
 #include <thread>  // NOLINT
 
-#include "paddle/fluid/framework/channel.h"
+#include "paddle/fluid/operators/reader/blocking_queue.h"
 #include "paddle/fluid/operators/reader/reader_op_registry.h"
 
 namespace paddle {
@@ -48,9 +48,9 @@ class MultiFileReader : public framework::ReaderBase {
   std::thread scheduler_;
   std::vector<std::thread> prefetchers_;
   size_t buffer_size_;
-  framework::Channel<size_t>* waiting_file_idx_;
-  framework::Channel<size_t>* available_thread_idx_;
-  framework::Channel<std::vector<framework::LoDTensor>>* buffer_;
+  reader::BlockingQueue<size_t>* waiting_file_idx_;
+  reader::BlockingQueue<size_t>* available_thread_idx_;
+  reader::BlockingQueue<std::vector<framework::LoDTensor>>* buffer_;
 };
 
 void MultiFileReader::ReadNext(std::vector<framework::LoDTensor>* out) {
@@ -73,17 +73,17 @@ bool MultiFileReader::HasNext() {
 
 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);
-  buffer_ =
-      framework::MakeChannel<std::vector<framework::LoDTensor>>(buffer_size_);
+  waiting_file_idx_ = new reader::BlockingQueue<size_t>(file_names_.size());
+  available_thread_idx_ = new reader::BlockingQueue<size_t>(thread_num);
+  buffer_ = new reader::BlockingQueue<std::vector<framework::LoDTensor>>(
+      buffer_size_);
 
   for (size_t i = 0; i < file_names_.size(); ++i) {
-    waiting_file_idx_->Send(&i);
+    waiting_file_idx_->Send(i);
   }
   waiting_file_idx_->Close();
   for (size_t i = 0; i < thread_num; ++i) {
-    available_thread_idx_->Send(&i);
+    available_thread_idx_->Send(i);
   }
 
   scheduler_ = std::thread([this] { ScheduleThreadFunc(); });
@@ -149,7 +149,7 @@ void MultiFileReader::PrefetchThreadFunc(std::string file_name,
       break;
     }
     try {
-      buffer_->Send(&ins);
+      buffer_->Send(std::move(ins));
     } catch (paddle::platform::EnforceNotMet e) {
       VLOG(5) << "WARNING: The buffer channel has been closed. The prefetch "
                  "thread of file '"
@@ -158,9 +158,7 @@ void MultiFileReader::PrefetchThreadFunc(std::string file_name,
     }
   }
 
-  try {
-    available_thread_idx_->Send(&thread_idx);
-  } catch (paddle::platform::EnforceNotMet e) {
+  if (!available_thread_idx_->Send(thread_idx)) {
     VLOG(5) << "WARNING: The available_thread_idx_ channel has been closed. "
                "Fail to send thread_idx.";
   }

From e2ca42408bc1580ffecbdb0b922f67eddd7aad94 Mon Sep 17 00:00:00 2001
From: fengjiayi <fengjiayi@baidu.com>
Date: Wed, 25 Apr 2018 19:54:46 +0800
Subject: [PATCH 3/7] Replace Channel in DoubleBufferReader with BlockingQueue

---
 .../reader/create_double_buffer_reader_op.cc      | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/paddle/fluid/operators/reader/create_double_buffer_reader_op.cc b/paddle/fluid/operators/reader/create_double_buffer_reader_op.cc
index 4372f23fc1..504e069b65 100644
--- a/paddle/fluid/operators/reader/create_double_buffer_reader_op.cc
+++ b/paddle/fluid/operators/reader/create_double_buffer_reader_op.cc
@@ -14,7 +14,7 @@
 
 #include <thread>  // NOLINT
 
-#include "paddle/fluid/framework/channel.h"
+#include "paddle/fluid/operators/reader/blocking_queue.h"
 #include "paddle/fluid/operators/reader/reader_op_registry.h"
 
 namespace paddle {
@@ -23,13 +23,13 @@ namespace reader {
 
 // 'Double buffer' means we shall maintain two batches of input data at the same
 // time. So the kCacheSize shoul be at least 2.
-static constexpr size_t kCacheSize = 2;
+static constexpr size_t kCacheSize = 3;
 // There will be two bacthes out of the channel during training:
 // 1. the one waiting to be sent to the channel
 // 2. the one just be received from the channel, which is also being used by
 // subsequent operators.
 // So the channel size should be kChacheSize - 2
-static constexpr size_t kChannelSize = 0;  // kCacheSize - 2
+static constexpr size_t kChannelSize = 1;  // kCacheSize - 2
 
 class DoubleBufferReader : public framework::DecoratedReader {
  public:
@@ -58,7 +58,7 @@ class DoubleBufferReader : public framework::DecoratedReader {
   bool HasNext() const;
 
   void StartPrefetcher() {
-    channel_ = framework::MakeChannel<size_t>(kChannelSize);
+    channel_ = new reader::BlockingQueue<size_t>(kChannelSize);
     prefetcher_ = std::thread([this] { PrefetchThreadFunc(); });
   }
 
@@ -74,7 +74,7 @@ class DoubleBufferReader : public framework::DecoratedReader {
   void PrefetchThreadFunc();
 
   std::thread prefetcher_;
-  framework::Channel<size_t>* channel_;
+  reader::BlockingQueue<size_t>* channel_;
   platform::Place place_;
   std::vector<std::vector<framework::LoDTensor>> cpu_tensor_cache_;
   std::vector<std::vector<framework::LoDTensor>> gpu_tensor_cache_;
@@ -185,10 +185,7 @@ void DoubleBufferReader::PrefetchThreadFunc() {
         gpu_batch[i].set_lod(cpu_batch[i].lod());
       }
     }
-    try {
-      size_t tmp = cached_tensor_id;
-      channel_->Send(&tmp);
-    } catch (paddle::platform::EnforceNotMet e) {
+    if (!channel_->Send(cached_tensor_id)) {
       VLOG(5) << "WARNING: The double buffer channel has been closed. The "
                  "prefetch thread will terminate.";
       break;

From 4cb63d845150b0b5b27505e174fe1023e3c0b229 Mon Sep 17 00:00:00 2001
From: fengjiayi <fengjiayi@baidu.com>
Date: Thu, 26 Apr 2018 00:53:44 +0800
Subject: [PATCH 4/7] Remove unnecessary header files

---
 paddle/fluid/operators/reader/blocking_queue.h | 2 --
 1 file changed, 2 deletions(-)

diff --git a/paddle/fluid/operators/reader/blocking_queue.h b/paddle/fluid/operators/reader/blocking_queue.h
index 4a54ccd5e8..5d0c27d30c 100644
--- a/paddle/fluid/operators/reader/blocking_queue.h
+++ b/paddle/fluid/operators/reader/blocking_queue.h
@@ -14,10 +14,8 @@
 
 #pragma once
 
-#include <algorithm>
 #include <condition_variable>  // NOLINT
 #include <deque>
-#include <memory>
 
 #include "paddle/fluid/platform/enforce.h"
 

From 304b6b71389e5bc035e6c04c6fdb76d2717f3588 Mon Sep 17 00:00:00 2001
From: fengjiayi <fengjiayi@baidu.com>
Date: Thu, 26 Apr 2018 11:11:25 +0800
Subject: [PATCH 5/7] Follow comments

---
 .../fluid/operators/reader/blocking_queue.h   | 37 +++++++++----------
 .../reader/create_double_buffer_reader_op.cc  | 17 ++-------
 .../fluid/operators/reader/open_files_op.cc   | 12 +-----
 3 files changed, 23 insertions(+), 43 deletions(-)

diff --git a/paddle/fluid/operators/reader/blocking_queue.h b/paddle/fluid/operators/reader/blocking_queue.h
index 5d0c27d30c..71684b1417 100644
--- a/paddle/fluid/operators/reader/blocking_queue.h
+++ b/paddle/fluid/operators/reader/blocking_queue.h
@@ -25,6 +25,11 @@ namespace reader {
 
 template <typename T>
 class BlockingQueue {
+  // BlockingQueue is for buffered reading and is supposed to use only the
+  // reader package. It is true that we could and we should have been using
+  // framework::Channel, but which has currently a deadlock bug. BlockingQueue
+  // is a workaround and a simplified version of framework::Channel as it
+  // doesn't support GPU and it implements on buffered blocking queue.
  public:
   explicit BlockingQueue(size_t capacity)
       : capacity_(capacity), closed_(false) {
@@ -37,26 +42,28 @@ class BlockingQueue {
     std::unique_lock<std::mutex> lock(mutex_);
     send_cv_.wait(lock, [&] { return queue_.size() < capacity_ || closed_; });
     if (closed_) {
+      VLOG(5)
+          << "WARNING: Sending an element to a closed reader::BlokcingQueue.";
       return false;
-    } else {
-      PADDLE_ENFORCE_LT(queue_.size(), capacity_);
-      queue_.push_back(elem);
-      receive_cv_.notify_one();
-      return true;
     }
+    PADDLE_ENFORCE_LT(queue_.size(), capacity_);
+    queue_.push_back(elem);
+    receive_cv_.notify_one();
+    return true;
   }
 
   bool Send(T&& elem) {
     std::unique_lock<std::mutex> lock(mutex_);
     send_cv_.wait(lock, [&] { return queue_.size() < capacity_ || closed_; });
     if (closed_) {
+      VLOG(5)
+          << "WARNING: Sending an element to a closed reader::BlokcingQueue.";
       return false;
-    } else {
-      PADDLE_ENFORCE_LT(queue_.size(), capacity_);
-      queue_.emplace_back(std::move(elem));
-      receive_cv_.notify_one();
-      return true;
     }
+    PADDLE_ENFORCE_LT(queue_.size(), capacity_);
+    queue_.emplace_back(std::move(elem));
+    receive_cv_.notify_one();
+    return true;
   }
 
   bool Receive(T* elem) {
@@ -86,16 +93,6 @@ class BlockingQueue {
     return closed_;
   }
 
-  bool CanSend() {
-    std::lock_guard<std::mutex> lock(mutex_);
-    return !closed_ && queue_.size() < capacity_;
-  }
-
-  bool CanReceive() {
-    std::lock_guard<std::mutex> lock(mutex_);
-    return !queue_.empty();
-  }
-
   size_t Cap() {
     std::lock_guard<std::mutex> lock(mutex_);
     return capacity_;
diff --git a/paddle/fluid/operators/reader/create_double_buffer_reader_op.cc b/paddle/fluid/operators/reader/create_double_buffer_reader_op.cc
index 504e069b65..3fdc31dfa5 100644
--- a/paddle/fluid/operators/reader/create_double_buffer_reader_op.cc
+++ b/paddle/fluid/operators/reader/create_double_buffer_reader_op.cc
@@ -55,8 +55,6 @@ class DoubleBufferReader : public framework::DecoratedReader {
   ~DoubleBufferReader() { EndPrefetcher(); }
 
  private:
-  bool HasNext() const;
-
   void StartPrefetcher() {
     channel_ = new reader::BlockingQueue<size_t>(kChannelSize);
     prefetcher_ = std::thread([this] { PrefetchThreadFunc(); });
@@ -139,17 +137,16 @@ class CreateDoubleBufferReaderOpMaker : public DecoratedReaderMakerBase {
 };
 
 void DoubleBufferReader::ReadNext(std::vector<framework::LoDTensor>* out) {
-  out->clear();
-  if (HasNext()) {
-    size_t cached_tensor_id;
-    channel_->Receive(&cached_tensor_id);
+  size_t cached_tensor_id;
+  if (channel_->Receive(&cached_tensor_id)) {
     if (platform::is_gpu_place(place_)) {
       *out = gpu_tensor_cache_[cached_tensor_id];
-      ctxs_[cached_tensor_id]->Wait();
     } else {
       // CPU place
       *out = cpu_tensor_cache_[cached_tensor_id];
     }
+  } else {
+    out->clear();
   }
 }
 
@@ -159,12 +156,6 @@ void DoubleBufferReader::ReInit() {
   StartPrefetcher();
 }
 
-bool DoubleBufferReader::HasNext() const {
-  while (!channel_->IsClosed() && !channel_->CanReceive()) {
-  }
-  return channel_->CanReceive();
-}
-
 void DoubleBufferReader::PrefetchThreadFunc() {
   VLOG(5) << "A new prefetch thread starts.";
   size_t cached_tensor_id = 0;
diff --git a/paddle/fluid/operators/reader/open_files_op.cc b/paddle/fluid/operators/reader/open_files_op.cc
index 461b56c7a4..91ad7d5658 100644
--- a/paddle/fluid/operators/reader/open_files_op.cc
+++ b/paddle/fluid/operators/reader/open_files_op.cc
@@ -37,7 +37,6 @@ class MultiFileReader : public framework::ReaderBase {
   ~MultiFileReader() { EndScheduler(); }
 
  private:
-  bool HasNext();
   void StartNewScheduler();
   void EndScheduler();
   void ScheduleThreadFunc();
@@ -54,9 +53,8 @@ class MultiFileReader : public framework::ReaderBase {
 };
 
 void MultiFileReader::ReadNext(std::vector<framework::LoDTensor>* out) {
-  out->clear();
-  if (HasNext()) {
-    buffer_->Receive(out);
+  if (!buffer_->Receive(out)) {
+    out->clear();
   }
 }
 
@@ -65,12 +63,6 @@ void MultiFileReader::ReInit() {
   StartNewScheduler();
 }
 
-bool MultiFileReader::HasNext() {
-  while (!buffer_->IsClosed() && !buffer_->CanReceive()) {
-  }
-  return buffer_->CanReceive();
-}
-
 void MultiFileReader::StartNewScheduler() {
   size_t thread_num = prefetchers_.size();
   waiting_file_idx_ = new reader::BlockingQueue<size_t>(file_names_.size());

From 17c51d69d12c09cf0af3baec2a8ebe3c9ec1de93 Mon Sep 17 00:00:00 2001
From: fengjiayi <fengjiayi@baidu.com>
Date: Thu, 26 Apr 2018 11:26:25 +0800
Subject: [PATCH 6/7] fix unit test error

---
 .../operators/reader/reader_blocking_queue_test.cc  | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/paddle/fluid/operators/reader/reader_blocking_queue_test.cc b/paddle/fluid/operators/reader/reader_blocking_queue_test.cc
index 07c22fe2bf..c0229f53f2 100644
--- a/paddle/fluid/operators/reader/reader_blocking_queue_test.cc
+++ b/paddle/fluid/operators/reader/reader_blocking_queue_test.cc
@@ -28,13 +28,6 @@ TEST(BlockingQueue, CapacityTest) {
   EXPECT_EQ(q.Cap(), cap);
 }
 
-TEST(BlockingQueue, CanSendTest) {
-  size_t cap = 1;
-  BlockingQueue<int> q(cap);
-  q.Send(1);
-  EXPECT_FALSE(q.CanSend());
-}
-
 void FirstInFirstOut(size_t queue_cap, size_t elem_num, size_t send_time_gap,
                      size_t receive_time_gap) {
   BlockingQueue<size_t> q(queue_cap);
@@ -83,9 +76,11 @@ TEST(BlockingQueue, SenderBlockingTest) {
   sender.join();
   EXPECT_EQ(send_count, queue_cap);
   std::vector<size_t> res;
-  while (q.CanReceive()) {
+  while (true) {
     size_t elem;
-    EXPECT_TRUE(q.Receive(&elem));
+    if (!q.Receive(&elem) {
+      break;
+    }
     res.push_back(elem);
   }
   EXPECT_EQ(res.size(), queue_cap);

From 8bd34664f12c61178a82dd1be535f4ae798a4540 Mon Sep 17 00:00:00 2001
From: fengjiayi <fengjiayi@baidu.com>
Date: Thu, 26 Apr 2018 11:27:17 +0800
Subject: [PATCH 7/7] fix unit test error

---
 paddle/fluid/operators/reader/reader_blocking_queue_test.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/paddle/fluid/operators/reader/reader_blocking_queue_test.cc b/paddle/fluid/operators/reader/reader_blocking_queue_test.cc
index c0229f53f2..7d1b381d56 100644
--- a/paddle/fluid/operators/reader/reader_blocking_queue_test.cc
+++ b/paddle/fluid/operators/reader/reader_blocking_queue_test.cc
@@ -78,7 +78,7 @@ TEST(BlockingQueue, SenderBlockingTest) {
   std::vector<size_t> res;
   while (true) {
     size_t elem;
-    if (!q.Receive(&elem) {
+    if (!q.Receive(&elem)) {
       break;
     }
     res.push_back(elem);