Simplify shutdown of AudioDevice's audio thread.

content/renderer/media/audio_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.
 //
 // Low-latency audio rendering unit utilizing audio output stream provided
 // by browser process through IPC.
 //
 // Relationship of classes.
 //
 //  AudioOutputController                AudioDevice
@@ skipping 139 matching lines @@
       return &socket_;
     }
     void Close() {
       // Close() should be thread-safe, obtain the lock.
       base::AutoLock auto_lock(lock_);
       socket_.Close();
     }
 
    private:
     // Magic required by ref_counted.h to avoid any code deleting the object
-    // accidently while there are references to it.
+    // accidentally while there are references to it.
     friend class base::RefCountedThreadSafe<AudioSocket>;
     ~AudioSocket() { }
 
     base::Lock lock_;
     base::SyncSocket socket_;
   };
 
   // Magic required by ref_counted.h to avoid any code deleting the object
   // accidently while there are references to it.
   friend class base::RefCountedThreadSafe<AudioDevice>;
   virtual ~AudioDevice();
 
   // Methods called on IO thread ----------------------------------------------
   // The following methods are tasks posted on the IO thread that needs to
   // be executed on that thread. They interact with AudioMessageFilter and
   // sends IPC messages on that thread.
   void InitializeOnIOThread(const AudioParameters& params);
   void PlayOnIOThread();
   void PauseOnIOThread(bool flush);
-  void ShutDownOnIOThread(base::WaitableEvent* completion);
+  void ShutDownOnIOThread();
   void SetVolumeOnIOThread(double volume);
 
   void Send(IPC::Message* message);
 
   // Method called on the audio thread ----------------------------------------
   // Calls the client's callback for rendering audio.
   // Returns actual number of filled frames that callback returned. This length
   // is passed to host at the end of the shared memory (i.e. buffer). In case of
   // continuous stream host just ignores it and assumes buffer is always filled
   // to its capacity.
@@ skipping 22 matching lines @@
 
   // The client stores the last reported audio delay in this member.
   // The delay shall reflect the amount of audio which still resides in
   // the output buffer, i.e., the expected audio output delay.
   int audio_delay_milliseconds_;
 
   // The current volume scaling [0.0, 1.0] of the audio stream.
   double volume_;
 
   // Callbacks for rendering audio occur on this thread.
+  // Must only be modified on the IO thread and when the thread is not running.
   scoped_ptr<base::DelegateSimpleThread> audio_thread_;
 
   // Cached audio message filter (lives on the main render thread).
   scoped_refptr<AudioMessageFilter> filter_;
 
   // Our stream ID on the message filter. Only accessed on the IO thread.
+  // Must only be modified on the IO thread.
   int32 stream_id_;
 
   // State of Play() / Pause() calls before OnLowLatencyCreated() is called.
   bool play_on_start_;
 
   // Set to |true| when OnLowLatencyCreated() is called.
   // Set to |false| when ShutDownOnIOThread() is called.
   // This is for use with play_on_start_ to track Play() / Pause() state.
+  // Must only be touched from the IO thread.
   bool is_started_;
 
   // Data transfer between browser and render process uses a combination
   // of sync sockets and shared memory to provide lowest possible latency.
+  // These variables must only be set on the IO thread while the audio_thread_
+  // is not running.
   base::SharedMemoryHandle shared_memory_handle_;
   scoped_refptr<AudioSocket> audio_socket_;
   int memory_length_;
 
-  // Protects lifetime of:
-  // audio_socket_
-  // audio_thread_
-  base::Lock lock_;
-
   DISALLOW_COPY_AND_ASSIGN(AudioDevice);
 };
 
 #endif  // CONTENT_RENDERER_MEDIA_AUDIO_DEVICE_H_