Fix data race in AudioDestination.cpp

third_party/WebKit/Source/platform/audio/AudioDestination.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 67 matching lines @@
   // the WebAudio rendering pipe line on the web thread.
   void RequestRenderOnWebThread(size_t frames_requested,
                                 size_t frames_to_render,
                                 double delay,
                                 double delay_timestamp,
                                 size_t prior_frames_skipped);
 
   virtual void Start();
   virtual void Stop();
 
   size_t CallbackBufferSize() const { return callback_buffer_size_; }

[nhiroki, 2017/05/01 01:56:39]

|callback_buffer_size_| must be accessed by the main thread. Can we have a
comment about it and/or a thread check (i.e., DCHECK(WTF::IsMainThread()))?

[hongchan, 2017/05/01 16:43:08]

Done.

   bool IsPlaying() { return is_playing_; }

[nhiroki, 2017/05/01 01:56:39]

ditto.

[hongchan, 2017/05/01 16:43:08]

Done.

 
   double SampleRate() const { return web_audio_device_->SampleRate(); }

[nhiroki, 2017/05/01 01:56:39]

ditto.

[hongchan, 2017/05/01 16:43:08]

Done.

 
   // Returns the audio buffer size in frames used by the underlying audio
   // hardware.
   int FramesPerBuffer() const { return web_audio_device_->FramesPerBuffer(); }

[nhiroki, 2017/05/01 01:56:39]

ditto.

[hongchan, 2017/05/01 16:43:08]

Done.

 
   // The information from the actual audio hardware. (via Platform::current)
   static float HardwareSampleRate();
   static unsigned long MaxChannelCount();
 
  private:
   // Check if the buffer size chosen by the WebAudioDevice is too large.
   bool CheckBufferSize();
 
   size_t HardwareBufferSize();
 
   bool IsRenderingThread();
 
+  // Accessed by the main thread.
   std::unique_ptr<WebAudioDevice> web_audio_device_;
   const unsigned number_of_output_channels_;
   size_t callback_buffer_size_;
   bool is_playing_;
 
-  // Rendering thread for WebAudio graph.
+  // Accessed by device and rendering threads: resolves the buffer size mismatch
+  // between the WebAudio engine and the callback function from the actual audio
+  // device.
+  std::unique_ptr<PushPullFIFO> fifo_;
+
+  // Accessed by the device thread. Rendering thread for WebAudio graph.
   std::unique_ptr<WebThread> rendering_thread_;
 
-  // Accessed by both threads: resolves the buffer size mismatch between the
-  // WebAudio engine and the callback function from the actual audio device.
-  std::unique_ptr<PushPullFIFO> fifo_;
-
   // Accessed by device thread: to pass the data from FIFO to the device.
   RefPtr<AudioBus> output_bus_;
 
   // Accessed by rendering thread: to push the rendered result from WebAudio
   // graph into the FIFO.
   RefPtr<AudioBus> render_bus_;
 
   // Accessed by rendering thread: the render callback function of WebAudio
   // engine. (i.e. DestinationNode)
   AudioIOCallback& callback_;
 
   // Accessed by rendering thread.
   size_t frames_elapsed_;
 };
 
 }  // namespace blink
 
 #endif  // AudioDestination_h