Deliver RenderCallbackErrors even when mixer inputs are paused.

media/base/audio_renderer_mixer.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.
 
 #ifndef MEDIA_BASE_AUDIO_RENDERER_MIXER_H_
 #define MEDIA_BASE_AUDIO_RENDERER_MIXER_H_
 
 #include <map>
 
 #include "base/synchronization/lock.h"
 #include "base/time/time.h"
 #include "media/base/audio_converter.h"
 #include "media/base/audio_renderer_sink.h"
 
 namespace media {
 
 // Mixes a set of AudioConverter::InputCallbacks into a single output stream
 // which is funneled into a single shared AudioRendererSink; saving a bundle
 // on renderer side resources.
 class MEDIA_EXPORT AudioRendererMixer
     : NON_EXPORTED_BASE(public AudioRendererSink::RenderCallback) {
  public:
   AudioRendererMixer(const AudioParameters& input_params,
                      const AudioParameters& output_params,
                      const scoped_refptr<AudioRendererSink>& sink);
   virtual ~AudioRendererMixer();
 
   // Add or remove a mixer input from mixing; called by AudioRendererMixerInput.
-  void AddMixerInput(AudioConverter::InputCallback* input,
-                     const base::Closure& error_cb);
+  void AddMixerInput(AudioConverter::InputCallback* input);
   void RemoveMixerInput(AudioConverter::InputCallback* input);
 
+  // Since errors may occur even when no inputs are playing, an error callback
+  // must be registered separately from adding a mixer.
+  void RegisterErrorCallback(AudioConverter::InputCallback* input,
+                             const base::Closure& error_cb);
+  void UnregisterErrorCallback(AudioConverter::InputCallback* input);
+
   void set_pause_delay_for_testing(base::TimeDelta delay) {
     pause_delay_ = delay;
   }
 
  private:
   // AudioRendererSink::RenderCallback implementation.
   virtual int Render(AudioBus* audio_bus,
                      int audio_delay_milliseconds) OVERRIDE;
   virtual void OnRenderError() OVERRIDE;
 
   // Output sink for this mixer.
   scoped_refptr<AudioRendererSink> audio_sink_;
 
-  // Set of mixer inputs to be mixed by this mixer.  Access is thread-safe
-  // through |mixer_inputs_lock_|.
+  // ---------------[ All variables below protected by |lock_| ]---------------
+  base::Lock lock_;
+
+  // Set of error callbacks used by this mixer.
   typedef std::map<AudioConverter::InputCallback*, base::Closure>
-      AudioRendererMixerInputSet;
-  AudioRendererMixerInputSet mixer_inputs_;
-  base::Lock mixer_inputs_lock_;
+      AudioRendererMixerErrorCallbackMap;
+  AudioRendererMixerErrorCallbackMap error_callbacks_;
 
   // Handles mixing and resampling between input and output parameters.
   AudioConverter audio_converter_;
 
   // Handles physical stream pause when no inputs are playing.  For latency
   // reasons we don't want to immediately pause the physical stream.
   base::TimeDelta pause_delay_;
   base::TimeTicks last_play_time_;
   bool playing_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioRendererMixer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_AUDIO_RENDERER_MIXER_H_