Tab Audio Capture: Browser-side connect/disconnect functionality.

media/audio/audio_output_controller.h

Index: media/audio/audio_output_controller.h
diff --git a/media/audio/audio_output_controller.h b/media/audio/audio_output_controller.h
index 762a9483d0fb51d1bdeed0cfa08a042508bab368..36461e1aee5a5a9f7d5d60bdfdf3fa18b377f257 100644
--- a/media/audio/audio_output_controller.h
+++ b/media/audio/audio_output_controller.h
@@ -65,7 +65,6 @@ namespace media {
 
 class MEDIA_EXPORT AudioOutputController
     : public base::RefCountedThreadSafe<AudioOutputController>,
-      public AudioOutputStream::AudioSourceCallback,
       NON_EXPORTED_BASE(public AudioManager::AudioDeviceListener)  {
  public:
   // An event handler that receives events from the AudioOutputController. The
@@ -139,21 +138,27 @@ class MEDIA_EXPORT AudioOutputController
   // Sets the volume of the audio output stream.
   void SetVolume(double volume);
 
-  // AudioSourceCallback implementation.
-  virtual int OnMoreData(AudioBus* dest,
-                         AudioBuffersState buffers_state) OVERRIDE;
-  virtual int OnMoreIOData(AudioBus* source,
-                           AudioBus* dest,
-                           AudioBuffersState buffers_state) OVERRIDE;
-  virtual void OnError(AudioOutputStream* stream, int code) OVERRIDE;
-  virtual void WaitTillDataReady() OVERRIDE;
-
   // AudioDeviceListener implementation.  When called AudioOutputController will
   // shutdown the existing |stream_|, transition to the kRecreating state,
   // create a new stream, and then transition back to an equivalent state prior
   // to being called.
   virtual void OnDeviceChange() OVERRIDE;
 
+  // Accessor to audio output parameters.
+  const AudioParameters& params() const { return params_; }
+
+  // Stops the normal audio output stream and creates an AudioSourceCallback to
+  // provide audio data to some other destination.  The given object will always
+  // return data when OnMoreData() is invoked, even if the underlying
+  // implementation is paused/stopped.  AudioOutputController retains ownership
+  // of the returned object.
+  AudioOutputStream::AudioSourceCallback* Divert();
+
+  // Restores normal audio output behavior for the current playback state.
+  // |asc| is the pointer returned by the previous call to Divert() and becomes
+  // invalid once this method is called.
+  void Revert(AudioOutputStream::AudioSourceCallback* asc);
+
  protected:
     // Internal state of the source.
   enum State {
@@ -172,6 +177,61 @@ class MEDIA_EXPORT AudioOutputController
   virtual ~AudioOutputController();
 
  private:
+  // An AudioSourceCallback that allows passing around the underlying SyncReader

[DaleCurtis, 2012/12/12 01:29:15]

Move to CC file?

[miu, 2012/12/12 03:13:39]

Done.

+  // data source between consumers of the data.  It does this in a "pass or
+  // delayed pass" scheme that ensures synchronization between timing-sensitive
+  // threads is effectively non-blocking.  In addition, Glue ensures that only
+  // one consumer is pulling data from the SyncReader at a time.
+  class Glue

[DaleCurtis, 2012/12/12 01:29:15]

A better name would be nice.

[miu, 2012/12/12 03:13:39]

Done.  s/Glue/SourceSharingCallback/

+      : public AudioOutputStream::AudioSourceCallback,
+        public base::RefCountedThreadSafe<Glue> {

[DaleCurtis, 2012/12/12 01:29:15]

Why does this need refcounting?

[miu, 2012/12/12 03:13:39]

An instance has to live until the "pass" completes, either on the current thread
or the hardware audio thread.  In other words, we need to be able to orphan an
instance.

I tried coding up a way to have the instance self-delete after a pass, but this
began to get complex, and I was pretty much reinventing this code:
base::Bind(&DoDelayedPass, this, other)

+   public:
+    Glue(AudioOutputController* controller, SyncReader* source);
+
+    // Pass the SyncReader to another instance as soon as possible.
+    void PassSoon(const scoped_refptr<Glue>& receiver);
+
+    // AudioSourceCallback implementation.
+    virtual int OnMoreData(AudioBus* dest_bus,
+                           AudioBuffersState buffers_state) OVERRIDE;
+    virtual int OnMoreIOData(AudioBus* source_bus,
+                             AudioBus* dest_bus,
+                             AudioBuffersState buffers_state) OVERRIDE;
+    virtual void OnError(AudioOutputStream* stream, int code) OVERRIDE;
+    virtual void WaitTillDataReady() OVERRIDE;
+
+   private:
+    friend class base::RefCountedThreadSafe<Glue>;
+    virtual ~Glue();
+
+    // Take over reading from |source|.
+    void ReceiveSource(SyncReader* source);
+
+    // Executes a delayed pass (i.e., a pass that was delayed because source_
+    // was in-use at the time PassSoon() was called).
+    void DoDelayedPassWithLockHeld(const scoped_refptr<Glue>& to);
+
+    // Access to parent/owner instance.
+    AudioOutputController* const controller_;
+
+    // Guards passing of SyncReader to another Glue instance.  The
+    // implementation should acquire lock_ for only very short operations since
+    // audio threads are timing-sensitive.
+    base::Lock lock_;
+
+    // Audio data source, or NULL if none yet.
+    SyncReader* source_;
+
+    // True while source_ is in-use without lock_ held.
+    bool is_reading_from_source_;
+
+    // When !delayed_pass_.is_null(), source_ is scheduled to be passed as soon
+    // as possible.
+    base::Closure delayed_pass_;
+
+    DISALLOW_COPY_AND_ASSIGN(Glue);
+  };
+
   // We are polling sync reader if data became available.
   static const int kPollNumAttempts;
   static const int kPollPauseInMilliseconds;
@@ -196,12 +256,19 @@ class MEDIA_EXPORT AudioOutputController
   // Signals event when done if it is not NULL.
   void DoStopCloseAndClearStream(base::WaitableEvent *done);
 
-  AudioManager* audio_manager_;
+  AudioManager* const audio_manager_;
+  const AudioParameters params_;
 
   // |handler_| may be called only if |state_| is not kClosed.
   EventHandler* handler_;
+
+  // AudioManager-owned stream.
   AudioOutputStream* stream_;
 
+  // Consumers of audio data which share sync_reader_.
+  scoped_refptr<Glue> stream_glue_;
+  scoped_refptr<Glue> divert_glue_;
+
   // The current volume of the audio stream.
   double volume_;
 
@@ -210,10 +277,6 @@ class MEDIA_EXPORT AudioOutputController
   // is not required for reading on the audio manager thread.
   State state_;
 
-  // The |lock_| must be acquired whenever we access |state_| from a thread
-  // other than the audio manager thread.
-  base::Lock lock_;
-
   // SyncReader is used only in low latency mode for synchronous reading.
   SyncReader* sync_reader_;
 
@@ -224,8 +287,6 @@ class MEDIA_EXPORT AudioOutputController
   // Number of times left.
   int number_polling_attempts_left_;
 
-  AudioParameters params_;
-
   // Used to post delayed tasks to ourselves that we can cancel.
   // We don't want the tasks to hold onto a reference as it will slow down
   // shutdown and force it to wait for the most delayed task.