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

content/renderer/media/media_stream_audio_track.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_TRACK_H_
 #define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_TRACK_H_
 
+#include <vector>
+
 #include "base/callback.h"
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "base/synchronization/lock.h"
 #include "content/renderer/media/media_stream_track.h"
-
-namespace webrtc {
-class AudioTrackInterface;
-}  // namespace webrtc
+#include "media/audio/audio_parameters.h"
 
 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);
 
+  // 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();
+  }
+
   // 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;
+  // call on the |sink| before the first chunk of audio is delivered.
+  void AddSink(MediaStreamAudioSink* sink);
 
-  // Remove a sink from the track.
-  // Called on the main render thread.
-  virtual void RemoveSink(MediaStreamAudioSink* sink) = 0;
-
-  // 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.
   // Called on the main render thread.
   // 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.
   void Stop() final;
 
+  // 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;
+
  protected:
   // Called by Stop() after the source has halted the flow of audio data.
   virtual void OnStop();
 
  private:
+  friend class MediaStreamAudioSource;
+
+  // 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 MediaStreamAudioSource 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 SetFormat(const media::AudioParameters& params);
+
+  // Called by the MediaStreamAudioSource to deliver audio data to this track,
+  // which in turn delivers the audio to one or more MediaStreamAudioSinks.
+  void DeliverDataToSinks(const media::AudioBus& audio_bus,
+                          base::TimeTicks reference_time);
+
+ private:
   // Callback provided to Start() which is run when the audio flow must halt.
   base::Closure stop_callback_;
 
+  // The current format of the audio passing through this track.
+  media::AudioParameters params_;
+
+  // Lock protects concurrent access to the sink lists below and the
+  // |is_enabled_| state, between the main thread and the audio thread.
+  mutable base::Lock lock_;
+
+  // Any sinks needing a call to MediaStreamAudioSink::OnSetFormat(), to be
+  // notified of the changed audio format, are placed in this list.  This
+  // includes sinks added via AddSink() that need to have an initial
+  // OnSetFormat() call before audio data is first delivered.  Sinks are moved
+  // from this list to |sinks_|.
+  std::vector<MediaStreamAudioSink*> pending_sinks_;
+
+  // Sinks that are up-to-date on the current audio format and are receiving
+  // audio data are placed in this list.
+  std::vector<MediaStreamAudioSink*> sinks_;
+
+  // When false, delivery of audio data is temporarily halted to the sinks.
+  bool is_enabled_;
+
+  // Provides weak pointers that are valid until Stop() is called.
+  base::WeakPtrFactory<MediaStreamAudioTrack> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(MediaStreamAudioTrack);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_TRACK_H_