Make AudioOutputDevice restartable and reinitializable

media/audio/audio_output_device.h

 // Copyright (c) 2012 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.
 //
+// TODO BEFORE COMMIT: Update documentation.
 // Audio rendering unit utilizing audio output stream provided by browser
 // process through IPC.
 //
 // Relationship of classes.
 //
 //  AudioOutputController                AudioOutputDevice
 //           ^                                ^
 //           |                                |
 //           v               IPC              v
 //    AudioRendererHost  <---------> AudioOutputIPC (AudioMessageFilter)
@@ skipping 58 matching lines @@
 #include "media/audio/audio_output_ipc.h"
 #include "media/audio/scoped_task_runner_observer.h"
 #include "media/base/audio_parameters.h"
 #include "media/base/audio_renderer_sink.h"
 #include "media/base/media_export.h"
 #include "media/base/output_device_info.h"
 
 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:
   // NOTE: Clients must call Initialize() before using.
   AudioOutputDevice(
       std::unique_ptr<AudioOutputIPC> ipc,
       const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner,
       int session_id,
       const std::string& device_id,
       const url::Origin& security_origin);
 
   // Request authorization to use the device specified in the constructor.
   void RequestDeviceAuthorization();
 
   // AudioRendererSink implementation.
   void Initialize(const AudioParameters& params,
-                  RenderCallback* callback) override;
+                  AudioRendererSink::RenderCallback* callback) override;
   void Start() override;
   void Stop() override;
   void Play() override;
   void Pause() override;
   bool SetVolume(double volume) override;
   OutputDeviceInfo GetOutputDeviceInfo() override;
 
   // Methods called on IO thread ----------------------------------------------
   // AudioOutputIPCDelegate methods.
   void OnStateChanged(AudioOutputIPCDelegateState state) override;
@@ skipping 16 matching lines @@
   enum State {
     IPC_CLOSED,       // No more IPCs can take place.
     IDLE,             // Not started.
     AUTHORIZING,      // Sent device authorization request, waiting for reply.
     AUTHORIZED,       // Successful device authorization received.
     CREATING_STREAM,  // Waiting for OnStreamCreated() to be called back.
     PAUSED,   // Paused.  OnStreamCreated() has been called.  Can Play()/Stop().
     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.
   // If the IO loop dies before we do, we shut down the audio thread from here.
   void WillDestroyCurrentMessageLoop() override;
 
   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
   // be accessed on the IO thread.
   std::unique_ptr<AudioOutputIPC> ipc_;
 
   // Current state (must only be accessed from the IO thread).  See comments for
   // State enum above.
   State state_;
 
@@ skipping 11 matching lines @@
   const std::string device_id_;
   const url::Origin security_origin_;
 
   // If |device_id_| is empty and |session_id_| is not, |matched_device_id_| is
   // received in OnDeviceAuthorized().
   std::string matched_device_id_;
 
   // 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_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioOutputDevice);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_DEVICE_H_