Redesign channel implementation for Select Op (#8814)

* Redesign channel implementation for Select Op

* Remove unecessary header

* Remove unnecessary comments

Author: abhinavarora

paddle/fluid/framework/channel.h

@@ -28,24 +28,19 @@ class Channel {
   virtual bool Send(T*) = 0;
   virtual bool Receive(T*) = 0;
   virtual size_t Cap() = 0;
+  virtual void Lock() = 0;
+  virtual void Unlock() = 0;
   virtual void Close() = 0;
   virtual ~Channel() {}
 };
 
 // Forward declaration of channel implementations.
-namespace details {
 template <typename T>
-class Buffered;
-template <typename T>
-class UnBuffered;
-}  // namespace details
+class ChannelImpl;
 
 template <typename T>
 Channel<T>* MakeChannel(size_t buffer_size) {
-  if (buffer_size > 0) {
-    return new details::Buffered<T>(buffer_size);
-  }
-  return new details::UnBuffered<T>();
+  return new ChannelImpl<T>(buffer_size);
 }
 
 template <typename T>
@@ -89,6 +84,19 @@ class ChannelHolder {
     if (IsInitialized()) holder_->Close();
   }
 
+  size_t Cap() {
+    if (IsInitialized()) return holder_->Cap();
+    return -1;
+  }
+
+  void Lock() {
+    if (IsInitialized()) holder_->Lock();
+  }
+
+  void Unlock() {
+    if (IsInitialized()) holder_->Unlock();
+  }
+
   inline bool IsInitialized() const { return holder_ != nullptr; }
 
   inline const std::type_index Type() {
@@ -106,6 +114,9 @@ class ChannelHolder {
     virtual const std::type_index Type() const = 0;
     virtual void* Ptr() const = 0;
     virtual void Close() = 0;
+    virtual void Lock() = 0;
+    virtual void Unlock() = 0;
+    virtual size_t Cap() = 0;
   };
 
   template <typename T>
@@ -115,11 +126,28 @@ class ChannelHolder {
     }
 
     virtual const std::type_index Type() const { return type_; }
+
     virtual void* Ptr() const { return static_cast<void*>(channel_.get()); }
+
     virtual void Close() {
       if (channel_) channel_->Close();
     }
 
+    virtual size_t Cap() {
+      if (channel_)
+        return channel_->Cap();
+      else
+        return -1;
+    }
+
+    virtual void Lock() {
+      if (channel_) channel_->Lock();
+    }
+
+    virtual void Unlock() {
+      if (channel_) channel_->Unlock();
+    }
+
     std::unique_ptr<Channel<T>> channel_;
     const std::type_index type_;
   };
@@ -131,5 +159,4 @@ class ChannelHolder {
 }  // namespace framework
 }  // namespace paddle
 
-#include "paddle/fluid/framework/details/buffered_channel.h"
-#include "paddle/fluid/framework/details/unbuffered_channel.h"
+#include "paddle/fluid/framework/channel_impl.h"

paddle/fluid/framework/channel_impl.h

@@ -0,0 +1,229 @@
+/* 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 <stddef.h>  // for size_t
+#include <atomic>
+#include <condition_variable>
+#include <deque>
+#include "paddle/fluid/framework/channel.h"
+#include "paddle/fluid/platform/enforce.h"
+
+namespace paddle {
+namespace framework {
+
+template <typename T>
+class ChannelImpl : public paddle::framework::Channel<T> {
+  friend Channel<T> *paddle::framework::MakeChannel<T>(size_t);
+  friend void paddle::framework::CloseChannel<T>(Channel<T> *);
+
+ public:
+  virtual bool Send(T *);
+  virtual bool Receive(T *);
+  virtual size_t Cap() { return cap_; }
+  virtual void Lock();
+  virtual void Unlock();
+  virtual void Close();
+
+  ChannelImpl(size_t);
+  virtual ~ChannelImpl();
+
+ private:
+  struct QueueMessage {
+    T *data;
+    std::condition_variable_any cond;
+    bool chan_closed = false;
+    bool completed = false;
+
+    QueueMessage(T *item) : data(item) {}
+
+    void Wait(std::unique_lock<std::recursive_mutex> &lock) {
+      cond.wait(lock, [this]() { return completed; });
+    }
+
+    void Notify() {
+      completed = true;
+      cond.notify_all();
+    }
+  };
+
+  bool send_return(bool value) {
+    send_ctr--;
+    destructor_cond_.notify_all();
+    return value;
+  }
+
+  bool recv_return(bool value) {
+    recv_ctr--;
+    destructor_cond_.notify_all();
+    return value;
+  }
+
+  size_t cap_;
+  std::recursive_mutex mu_;
+  bool closed_;
+  std::deque<T> buf_;
+  std::deque<std::shared_ptr<QueueMessage>> recvq;
+  std::deque<std::shared_ptr<QueueMessage>> sendq;
+  std::atomic<unsigned> send_ctr{0};
+  std::atomic<unsigned> recv_ctr{0};
+  std::condition_variable_any destructor_cond_;
+};
+
+template <typename T>
+ChannelImpl<T>::ChannelImpl(size_t capacity)
+    : cap_(capacity), closed_(false), send_ctr(0), recv_ctr(0) {
+  PADDLE_ENFORCE_GE(capacity, 0);
+}
+
+template <typename T>
+bool ChannelImpl<T>::Send(T *item) {
+  send_ctr++;
+  std::unique_lock<std::recursive_mutex> lock{mu_};
+
+  // If channel is closed, do nothing
+  if (closed_) {
+    lock.unlock();
+    // TODO(abhinavarora) Should panic on closed channel
+    return send_return(false);
+  }
+
+  // If there is a receiver, directly pass the value we want
+  // to send to the receiver, bypassing the channel buffer if any
+  if (!recvq.empty()) {
+    std::shared_ptr<QueueMessage> m = recvq.front();
+    recvq.pop_front();
+    // Do the data transfer
+    *(m->data) = std::move(*item);
+    // Wake up the blocked process and unlock
+    m->Notify();
+    lock.unlock();
+    return send_return(true);
+  }
+
+  // Unbuffered channel will always bypass this
+  // If buffered channel has space in buffer,
+  // write the element to the buffer.
+  if (buf_.size() < cap_) {
+    // Copy to buffer
+    buf_.push_back(std::move(*item));
+    // Release lock and return true
+    lock.unlock();
+    return send_return(true);
+  }
+
+  // Block on channel, because some receiver will complete
+  // the operation for us
+  auto m = std::make_shared<QueueMessage>(item);
+  sendq.push_back(m);
+  m->Wait(lock);
+  // TODO(abhinavarora) Should panic on closed channel
+  return send_return(!m->chan_closed);
+}
+
+template <typename T>
+bool ChannelImpl<T>::Receive(T *item) {
+  recv_ctr++;
+  std::unique_lock<std::recursive_mutex> lock{mu_};
+
+  // If channel is closed and buffer is empty or
+  // channel is unbuffered
+  if (closed_ && buf_.empty()) {
+    lock.unlock();
+    return recv_return(false);
+  }
+
+  // If there is a sender, directly receive the value we want
+  // from the sender, bypassing the channel buffer if any
+  if (!sendq.empty()) {
+    std::shared_ptr<QueueMessage> m = sendq.front();
+    sendq.pop_front();
+    // Do the data transfer
+    *item = std::move(*(m->data));
+    // Wake up the blocked process and unlock
+    m->Notify();
+    lock.unlock();
+    return recv_return(true);
+  }
+
+  // If this is a buffered channel and there are items in buffer
+  if (buf_.size() > 0) {
+    // Directly read from buffer
+    *item = std::move(buf_.front());
+    buf_.pop_front();
+    // Release lock and return true
+    lock.unlock();
+    return recv_return(true);
+  }
+
+  // No sender available, block on this channel
+  // Some receiver will complete the option for us
+  auto m = std::make_shared<QueueMessage>(item);
+  recvq.push_back(m);
+  m->Wait(lock);
+
+  return recv_return(!m->chan_closed);
+}
+
+template <typename T>
+void ChannelImpl<T>::Lock() {
+  mu_.lock();
+}
+
+template <typename T>
+void ChannelImpl<T>::Unlock() {
+  mu_.unlock();
+}
+
+template <typename T>
+void ChannelImpl<T>::Close() {
+  std::unique_lock<std::recursive_mutex> lock{mu_};
+
+  if (closed_) {
+    // TODO(abhinavarora): closing an already closed channel should panic
+    lock.unlock();
+    return;
+  }
+
+  closed_ = true;
+
+  // Empty the readers
+  while (!recvq.empty()) {
+    std::shared_ptr<QueueMessage> m = recvq.front();
+    recvq.pop_front();
+    m->chan_closed = true;
+    m->Notify();
+  }
+
+  // Empty the senders
+  while (!sendq.empty()) {
+    std::shared_ptr<QueueMessage> m = sendq.front();
+    sendq.pop_front();
+    m->chan_closed = true;
+    m->Notify();
+  }
+}
+
+template <typename T>
+ChannelImpl<T>::~ChannelImpl() {
+  Close();
+  // The destructor must wait for all readers and writers to complete their task
+  // The channel has been closed, so we will not accept new readers and writers
+  std::unique_lock<std::recursive_mutex> lock{mu_};
+  destructor_cond_.wait(lock,
+                        [this]() { return send_ctr == 0 && recv_ctr == 0; });
+}
+
+}  // namespace framework
+}  // namespace paddle