Make AudioOutputDevice restartable and reinitializable

media/audio/audio_output_device.h

Index: media/audio/audio_output_device.h
diff --git a/media/audio/audio_output_device.h b/media/audio/audio_output_device.h
index 532f45fe4a13eeb6b8b2884292e28652da3690f1..45235ee73e260b0ce71c0c7e2935da8b0264bc02 100644
--- a/media/audio/audio_output_device.h
+++ b/media/audio/audio_output_device.h
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
+// TODO BEFORE COMMIT: Update documentation.
 // Audio rendering unit utilizing audio output stream provided by browser
 // process through IPC.
 //
@@ -80,7 +81,8 @@
 namespace media {
 
 class MEDIA_EXPORT AudioOutputDevice
-    : NON_EXPORTED_BASE(public AudioRendererSink),
+    : NON_EXPORTED_BASE(public RestartableAudioRendererSink),
+      NON_EXPORTED_BASE(public AudioRendererSink::RenderCallback),
       NON_EXPORTED_BASE(public AudioOutputIPCDelegate),
       NON_EXPORTED_BASE(public ScopedTaskRunnerObserver) {
  public:
@@ -97,7 +99,7 @@ class MEDIA_EXPORT AudioOutputDevice
 
   // AudioRendererSink implementation.
   void Initialize(const AudioParameters& params,
-                  RenderCallback* callback) override;
+                  AudioRendererSink::RenderCallback* callback) override;
   void Start() override;
   void Stop() override;
   void Play() override;
@@ -134,15 +136,24 @@ class MEDIA_EXPORT AudioOutputDevice
     PLAYING,  // Playing back.  Can Pause()/Stop().
   };
 
+  // media::AudioRendererSink::RenderCallback implementation.
+  // These two functions are called on the audio worker thread and passes calls
+  // through to |callback_| if it exists.
+  int Render(media::AudioBus* audio_bus,
+             uint32_t frames_delayed,
+             uint32_t frames_skipped) override;
+  void OnRenderError() override;
+
   // Methods called on IO thread ----------------------------------------------
   // The following methods are tasks posted on the IO thread that need to
   // be executed on that thread.  They use AudioOutputIPC to send IPC messages
   // upon state changes.
   void RequestDeviceAuthorizationOnIOThread();
-  void CreateStreamOnIOThread(const AudioParameters& params);
+  void InitializeOnIOThread(const AudioParameters& params);
+  void CreateStreamOnIOThread();
   void PlayOnIOThread();
   void PauseOnIOThread();
-  void ShutDownOnIOThread();
+  void StopOnIOThread();
   void SetVolumeOnIOThread(double volume);
 
   // base::MessageLoop::DestructionObserver implementation for the IO loop.
@@ -151,7 +162,8 @@ class MEDIA_EXPORT AudioOutputDevice
 
   AudioParameters audio_parameters_;
 
-  RenderCallback* callback_;
+  base::Lock callback_lock_;
+  AudioRendererSink::RenderCallback* callback_;

[o1ka, 2016/05/03 15:47:32]

Probably store it as atomic word => get rid of the lock?

[Henrik Grunell, 2016/05/04 09:05:12]

We need to hold on to a lock while calling e.g. Render() so that the callee
can't call Stop() and then expect no callbacks, while we could actually be
executing one at that time.

 
   // A pointer to the IPC layer that takes care of sending requests over to
   // the AudioRendererHost.  Only valid when state_ != IPC_CLOSED and must only
@@ -183,20 +195,10 @@ class MEDIA_EXPORT AudioOutputDevice
   // Our audio thread callback class.  See source file for details.
   class AudioThreadCallback;
 
-  // In order to avoid a race between OnStreamCreated and Stop(), we use this
-  // guard to control stopping and starting the audio thread.
-  base::Lock audio_thread_lock_;
+  // The audio thread implementation.
   AudioDeviceThread audio_thread_;
   std::unique_ptr<AudioOutputDevice::AudioThreadCallback> audio_callback_;

[o1ka, 2016/05/03 15:47:32]

Could we probably rename "callback_" into "render_callback_" and
"audio_callback_" into "audio_thread_callback_", or something like this, to
improve readability? WDYT?

[Henrik Grunell, 2016/05/04 09:05:12]

Good idea. Done.

 
-  // Temporary hack to ignore OnStreamCreated() due to the user calling Stop()
-  // so we don't start the audio thread pointing to a potentially freed
-  // |callback_|.
-  //
-  // TODO(scherkus): Replace this by changing AudioRendererSink to either accept
-  // the callback via Start(). See http://crbug.com/151051 for details.
-  bool stopping_hack_;
-
   base::WaitableEvent did_receive_auth_;
   AudioParameters output_params_;
   OutputDeviceStatus device_status_;