Improve thread creation in plaform/audio/AudioDestination

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

Index: third_party/WebKit/Source/platform/audio/AudioDestination.h
diff --git a/third_party/WebKit/Source/platform/audio/AudioDestination.h b/third_party/WebKit/Source/platform/audio/AudioDestination.h
index 64797f225cfe21ea6e33bd4cbc787e338fb64ed7..b1dd817cff6188d32b2c936b832d50f361428ade 100644
--- a/third_party/WebKit/Source/platform/audio/AudioDestination.h
+++ b/third_party/WebKit/Source/platform/audio/AudioDestination.h
@@ -85,14 +85,16 @@ class PLATFORM_EXPORT AudioDestination : public WebAudioDevice::RenderCallback {
   virtual void Start();
   virtual void Stop();
 
-  size_t CallbackBufferSize() const { return callback_buffer_size_; }
-  bool IsPlaying() { return is_playing_; }
+  // Getters must be accessed from the main thread.
+  size_t CallbackBufferSize() const;
+  bool IsPlaying();
 
+  // TODO(hongchan): this should not be by the rendering thread.

[haraken, 2017/05/02 05:02:07]

be called

[hongchan, 2017/05/02 16:49:41]

Done.

   double SampleRate() const { return web_audio_device_->SampleRate(); }
 
   // Returns the audio buffer size in frames used by the underlying audio
   // hardware.
-  int FramesPerBuffer() const { return web_audio_device_->FramesPerBuffer(); }
+  int FramesPerBuffer() const;
 
   // The information from the actual audio hardware. (via Platform::current)
   static float HardwareSampleRate();
@@ -106,12 +108,13 @@ class PLATFORM_EXPORT AudioDestination : public WebAudioDevice::RenderCallback {
 
   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 the device thread. Rendering thread for WebAudio graph.

[haraken, 2017/05/02 05:02:07]

The rendering_thread_ is accessed by the main thread, right?

[hongchan, 2017/05/02 16:49:41]

Its life cycle is governed by the main thread, but it is mostly used (accessed)
by the device thread.

[haraken, 2017/05/03 09:18:01]

Makes sense. We could probably unify terms between 'device thread' and
'rendering thread'.

   std::unique_ptr<WebThread> rendering_thread_;
 
   // Accessed by both threads: resolves the buffer size mismatch between the