Introduce PushPullFIFO class and remove other FIFOs

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

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
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  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
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@@ skipping 13 matching lines @@
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  */
 
 #ifndef AudioDestination_h
 #define AudioDestination_h
 
 #include "platform/audio/AudioBus.h"
 #include "platform/audio/AudioIOCallback.h"
-#include "platform/audio/AudioSourceProvider.h"
 #include "public/platform/WebAudioDevice.h"
 #include "public/platform/WebVector.h"
 #include "wtf/Allocator.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/text/WTFString.h"
 #include <memory>
 
 namespace blink {
 
-class AudioPullFIFO;
+class PushPullFIFO;
 class SecurityOrigin;
 
 // The AudioDestination class is an audio sink interface between the media
 // renderer and the Blink's WebAudio module. It has a FIFO to adapt the
 // different processing block sizes of WebAudio renderer and actual hardware
 // audio callback.
-class PLATFORM_EXPORT AudioDestination : public WebAudioDevice::RenderCallback,
-                                         public AudioSourceProvider {
+class PLATFORM_EXPORT AudioDestination : public WebAudioDevice::RenderCallback {
   USING_FAST_MALLOC(AudioDestination);
   WTF_MAKE_NONCOPYABLE(AudioDestination);
 
  public:
   AudioDestination(AudioIOCallback&,
                    unsigned numberOfOutputChannels,
                    float sampleRate,
                    PassRefPtr<SecurityOrigin>);
   ~AudioDestination() override;
 
   static std::unique_ptr<AudioDestination> create(
       AudioIOCallback&,
       unsigned numberOfOutputChannels,
       float sampleRate,
       PassRefPtr<SecurityOrigin>);
 
   // The actual render function (WebAudioDevice::RenderCallback) isochronously
   // invoked by the media renderer.
   void render(const WebVector<float*>& destinationData,
               size_t numberOfFrames,
               double delay,
               double delayTimestamp,
               size_t priorFramesSkipped) override;
 
-  // AudioSourceProvider (FIFO)
-  void provideInput(AudioBus* outputBus, size_t framesToProcess) override;
-
   virtual void start();
   virtual void stop();
 
   size_t callbackBufferSize() const { return m_callbackBufferSize; }
   float sampleRate() const { return m_sampleRate; }
   bool isPlaying() { return m_isPlaying; }
 
   // The information from the actual audio hardware. (via Platform::current)
   static float hardwareSampleRate();
   static unsigned long maxChannelCount();
 
  private:
   std::unique_ptr<WebAudioDevice> m_webAudioDevice;
   unsigned m_numberOfOutputChannels;
   size_t m_callbackBufferSize;
   float m_sampleRate;
   bool m_isPlaying;
 
   // The render callback function of WebAudio engine. (i.e. DestinationNode)
   AudioIOCallback& m_callback;
 
+  // To pass the data from FIFO to the audio device callback.

[Raymond Toy, 2017/01/30 20:59:27]

nit: This comment is a bit unclear.  Maybe say m_outputBus holds the data that
will be sent to the audio device callback?

   RefPtr<AudioBus> m_outputBus;
-  std::unique_ptr<AudioPullFIFO> m_fifo;
+
+  // To push the rendered result from WebAudio graph into the FIFO.

[Raymond Toy, 2017/01/30 20:59:27]

Likewise, m_renderBus is used to hold the data that the WebAudio graph will
write to the FIFO.

+  RefPtr<AudioBus> m_renderBus;
+
+  // Resolves the buffer size mismatch between the WebAudio engine and
+  // the callback function from the actual audio device.

[Raymond Toy, 2017/01/30 20:59:28]

I think you can just say this is a FIFO between the WebAudio and the audio
device.  There isn't always a size mismatch.

+  std::unique_ptr<PushPullFIFO> m_fifo;
 
   size_t m_framesElapsed;
   AudioIOPosition m_outputPosition;
   base::TimeTicks m_outputPositionReceivedTimestamp;
 
   // Calculate the optimum buffer size for a given platform. Return false if the
   // buffer size calculation fails.
   bool calculateBufferSize();
 
   size_t hardwareBufferSize();
 };
 
 }  // namespace blink
 
 #endif  // AudioDestination_h