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..a76432f3c4bf89aa30969ac9bd5840b28d474b8c 100644
--- a/media/audio/audio_output_device.h
+++ b/media/audio/audio_output_device.h
@@ -45,8 +45,6 @@
 // 1. Creating thread.
 //    Must be the main render thread.
 // 2. Control thread (may be the main render thread or another thread).
-//    The methods: Start(), Stop(), Play(), Pause(), SetVolume()
-//    must be called on the same thread.
 // 3. IO thread (internal implementation detail - not exposed to public API)
 //    The thread within which this class receives all the IPC messages and
 //    IPC communications can only happen in this thread.
@@ -56,8 +54,7 @@
 //    the audio layer in the browser process using sync sockets and shared
 //    memory.
 //
-// Implementation notes:
-// - The user must call Stop() before deleting the class instance.
+// NOTE: The user must call Stop() before deleting the class instance.
 
 #ifndef MEDIA_AUDIO_AUDIO_OUTPUT_DEVICE_H_
 #define MEDIA_AUDIO_AUDIO_OUTPUT_DEVICE_H_
@@ -80,7 +77,8 @@
 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 +95,7 @@ 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 +132,24 @@ 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 |render_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 +158,11 @@ class MEDIA_EXPORT AudioOutputDevice
 
   AudioParameters audio_parameters_;
 
-  RenderCallback* callback_;
+  // |callback_lock_| protects |render_callback_|. When held, only accessing
+  // |render_callback_| is allowed. In particular, no calls must be made on
+  // |audio_thread_| for the risk of deadlocks.
+  base::Lock callback_lock_;
+  AudioRendererSink::RenderCallback* render_callback_;
 
   // 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
@@ -183,19 +194,10 @@ 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_;
-
-  // 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_;
+  std::unique_ptr<AudioOutputDevice::AudioThreadCallback>
+      audio_thread_callback_;
 
   base::WaitableEvent did_receive_auth_;
   AudioParameters output_params_;