MediaStream audio: Refactor 3 separate "glue" implementations into one.

content/renderer/media/media_stream_audio_track.h

Index: content/renderer/media/media_stream_audio_track.h
diff --git a/content/renderer/media/media_stream_audio_track.h b/content/renderer/media/media_stream_audio_track.h
index 0ef126b431a3af9bcdc0686f71ecd95a474214bc..c8c2b8482a8e90a042ebb1fd384ff1a69bd8336c 100644
--- a/content/renderer/media/media_stream_audio_track.h
+++ b/content/renderer/media/media_stream_audio_track.h
@@ -5,46 +5,50 @@
 #ifndef CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_TRACK_H_
 #define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_TRACK_H_
 
+#include <memory>
+
+#include "base/atomicops.h"
 #include "base/callback.h"
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/synchronization/lock.h"
+#include "base/threading/thread_checker.h"
+#include "content/renderer/media/media_stream_audio_deliverer.h"
 #include "content/renderer/media/media_stream_track.h"
 
-namespace webrtc {
-class AudioTrackInterface;
-}  // namespace webrtc
-
 namespace content {
 
 class MediaStreamAudioSink;
+class MediaStreamAudioSource;
 
-// TODO(miu): In a soon-upcoming set of refactoring changes, this class will
-// take on the functionality of managing sink connections and the audio data
-// flow between source and sinks.  The WebRTC-specific elements will then be
-// moved into a subclass.   http://crbug.com/577874
+// Provides the part of the audio pipeline delivering audio from a
+// MediaStreamAudioSource to one or more MediaStreamAudioSinks. An instance of
+// this class is owned by blink::WebMediaStreamTrack, and clients should use
+// From() to gain access to a MediaStreamAudioTrack.
 class CONTENT_EXPORT MediaStreamAudioTrack : public MediaStreamTrack {
  public:
   explicit MediaStreamAudioTrack(bool is_local_track);
 
-  // Subclasses must ensure the track is stopped (i.e., Stop() has been called
-  // at least once) before this destructor is invoked.
   ~MediaStreamAudioTrack() override;
 
   // Returns the MediaStreamAudioTrack instance owned by the given blink |track|
   // or null.
   static MediaStreamAudioTrack* From(const blink::WebMediaStreamTrack& track);
 
-  // Add a sink to the track. This function will trigger a OnSetFormat()
-  // call on the |sink|.
-  // Called on the main render thread.
-  virtual void AddSink(MediaStreamAudioSink* sink) = 0;
+  // Provides a weak reference to this MediaStreamAudioTrack which is
+  // invalidated when Stop() is called. The weak pointer may only be
+  // dereferenced on the main thread.
+  base::WeakPtr<MediaStreamAudioTrack> GetWeakPtr() {
+    return weak_factory_.GetWeakPtr();
+  }
 
-  // Remove a sink from the track.
-  // Called on the main render thread.
-  virtual void RemoveSink(MediaStreamAudioSink* sink) = 0;
+  // Add a sink to the track. This function will trigger a OnSetFormat()
+  // call on the |sink| before the first chunk of audio is delivered.
+  void AddSink(MediaStreamAudioSink* sink);
 
-  // TODO(tommi, xians): Remove this method.
-  // TODO(miu): See class-level TODO comment.  ;-)
-  virtual webrtc::AudioTrackInterface* GetAudioAdapter();
+  // Remove a sink from the track. When this method returns, the sink's
+  // OnSetFormat() and OnData() methods will not be called again on any thread.
+  void RemoveSink(MediaStreamAudioSink* sink);
 
   // Returns the output format of the capture source. May return an invalid
   // AudioParameters if the format is not yet available.
@@ -52,25 +56,60 @@ class CONTENT_EXPORT MediaStreamAudioTrack : public MediaStreamTrack {
   // TODO(tommi): This method appears to only be used by Pepper and in fact
   // does not appear to be necessary there.  We should remove it since it adds
   // to the complexity of all types of audio tracks+source implementations.
-  virtual media::AudioParameters GetOutputFormat() const = 0;
-
-  // Called to notify this track that the flow of audio data has started from
-  // the source.  |stop_callback| is run by Stop() when the source must halt the
-  // flow of audio data to this track.
-  void Start(const base::Closure& stop_callback);
+  // http://crbug.com/577874
+  media::AudioParameters GetOutputFormat() const;
 
   // Halts the flow of audio data from the source (and to the sinks), and then
-  // invokes OnStop() to perform any additional actions.
+  // notifies all sinks of the "ended" state.
   void Stop() final;
 
- protected:
-  // Called by Stop() after the source has halted the flow of audio data.
-  virtual void OnStop();
+  // MediaStreamTrack override.
+  void SetEnabled(bool enabled) override;
+
+  // Returns a unique class identifier. Some subclasses override and use this
+  // method to provide safe down-casting to their type.
+  virtual void* GetClassIdentifier() const;
+
+ private:
+  friend class MediaStreamAudioSource;
+  friend class MediaStreamAudioDeliverer<MediaStreamAudioTrack>;
+
+  // Called by MediaStreamAudioSource to notify this track that the flow of
+  // audio data has started from the source. |stop_callback| is run by Stop()
+  // when the source must halt the flow of audio data to this track.
+  void Start(const base::Closure& stop_callback);
+
+  // Called by the MediaStreamAudioDeliverer to notify this track of an audio
+  // format change. In turn, all MediaStreamAudioSinks will be notified before
+  // the next chunk of audio is delivered to them.
+  void OnSetFormat(const media::AudioParameters& params);
+
+  // Called by the MediaStreamAudioDeliverer to deliver audio data to this
+  // track, which in turn delivers the audio to one or more
+  // MediaStreamAudioSinks. While this track is disabled, silent audio will be
+  // delivered to the sinks instead of the content of |audio_bus|.
+  void OnData(const media::AudioBus& audio_bus, base::TimeTicks reference_time);
 
  private:
+  // In debug builds, check that all methods that could cause object graph
+  // or data flow changes are being called on the main thread.
+  base::ThreadChecker thread_checker_;
+
   // Callback provided to Start() which is run when the audio flow must halt.
   base::Closure stop_callback_;
 
+  // Manages sinks connected to this track and the audio format and data flow.
+  MediaStreamAudioDeliverer<MediaStreamAudioSink> deliverer_;
+
+  // While false (0), silent audio is delivered to the sinks.
+  base::subtle::Atomic32 is_enabled_;
+
+  // Buffer used to deliver silent audio data while this track is disabled.
+  std::unique_ptr<media::AudioBus> silent_bus_;
+
+  // Provides weak pointers that are valid until Stop() is called.
+  base::WeakPtrFactory<MediaStreamAudioTrack> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(MediaStreamAudioTrack);
 };