Fix start/stop of html5 audio stream and race condition when pausing.

content/renderer/media/audio_device.h

 // Copyright (c) 2011 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 63 matching lines @@
 #include "content/renderer/media/audio_message_filter.h"
 #include "media/audio/audio_parameters.h"
 
 class CONTENT_EXPORT AudioDevice
     : public AudioMessageFilter::Delegate,
       public base::DelegateSimpleThread::Delegate,
       public base::RefCountedThreadSafe<AudioDevice> {
  public:
   class CONTENT_EXPORT RenderCallback {
    public:
-    virtual void Render(const std::vector<float*>& audio_data,
-                        size_t number_of_frames,
-                        size_t audio_delay_milliseconds) = 0;
+    // Always fills entire buffer but returns actual number of frames it got
+    // from source. That actual number of frames is passed to host at the end
+    // of the shared memory (i.e. buffer), and host is free to use or ignore it.

[Chris Rogers, 2011/12/15 00:32:52]

nit: the implementation details of "shared memory" should not be mentioned at
this level in this comment because this method is an abstract interface and
AudioDevice is free to change its implementation.  The implementor of Render()
should not even be aware of "shared memory".  Instead we should just say that
Render() is expected to put number_of_frames of a continuous stream of PCM audio
data into audio_data.  If it doesn't have that much available then it should
return a value less than number_of_frames (otherwise just return
number_of_frames).  This can probably be worded better, but you get the idea.

But we can move the part describing details of "shared memory" down below to
FireRenderCallback().  Then you can remove the comment down there which says
"see comment on RenderCallback::Render()"

[enal1, 2011/12/15 16:54:40]

Done.

+    virtual size_t Render(const std::vector<float*>& audio_data,
+                          size_t number_of_frames,
+                          size_t audio_delay_milliseconds) = 0;
    protected:
     virtual ~RenderCallback() {}
   };
 
   // Methods called on main render thread -------------------------------------
 
   // Minimal constructor where Initialize() must be called later.
   AudioDevice();
 
   AudioDevice(size_t buffer_size,
@@ skipping 56 matching lines @@
   // sends IPC messages on that thread.
   void InitializeOnIOThread(const AudioParameters& params);
   void PlayOnIOThread();
   void PauseOnIOThread(bool flush);
   void ShutDownOnIOThread(base::WaitableEvent* completion);
   void SetVolumeOnIOThread(double volume);
 
   void Send(IPC::Message* message);
 
   // Method called on the audio thread (+ one call on the IO thread) ----------
-  // Calls the client's callback for rendering audio. There will also be one
-  // initial call on the IO thread before the audio thread has been created.
-  void FireRenderCallback(int16* data);
+  // Calls the client's callback for rendering audio.
+  // Returns actual number of filled frames, see comment on
+  // RenderCallback::Render().

[Chris Rogers, 2011/12/15 00:32:52]

See my comment above.

[enal1, 2011/12/15 16:54:40]

Done.

+  size_t FireRenderCallback(int16* data);
 
   // DelegateSimpleThread::Delegate implementation.
   virtual void Run() OVERRIDE;
 
   // Closes socket and joins with the audio thread.
   void ShutDownAudioThread();
 
   // Format
   size_t buffer_size_;  // in sample-frames
   int channels_;
@@ skipping 42 matching lines @@
 
   // Protects lifetime of:
   // socket_handle_
   // audio_thread_
   base::Lock lock_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioDevice);
 };
 
 #endif  // CONTENT_RENDERER_MEDIA_AUDIO_DEVICE_H_