Caching AudioOutputDevice instances in mixer manager

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 <stdint.h>
 
 #include <map>
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "base/synchronization/lock.h"
 #include "base/time/time.h"
 #include "media/base/audio_converter.h"
 #include "media/base/audio_renderer_sink.h"
 #include "media/base/loopback_audio_converter.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& output_params,
-                     const scoped_refptr<AudioRendererSink>& sink);
+                     scoped_refptr<AudioRendererSink> sink);
   ~AudioRendererMixer() override;
 
   // Add or remove a mixer input from mixing; called by AudioRendererMixerInput.
   void AddMixerInput(const AudioParameters& input_params,
                      AudioConverter::InputCallback* input);
   void RemoveMixerInput(const AudioParameters& input_params,
                         AudioConverter::InputCallback* input);
 
   // Since errors may occur even when no inputs are playing, an error callback
   // must be registered separately from adding a mixer input.  The same callback
@@ skipping 15 matching lines @@
   // AudioRendererSink::RenderCallback implementation.
   int Render(AudioBus* audio_bus,
              uint32_t frames_delayed,
              uint32_t frames_skipped) override;
   void OnRenderError() override;
 
   bool is_master_sample_rate(int sample_rate) {
     return sample_rate == output_params_.sample_rate();
   }
 
+  // Output parameters for this mixer.
+  const AudioParameters output_params_;
+
   // Output sink for this mixer.
-  scoped_refptr<AudioRendererSink> audio_sink_;
-
-  // Output parameters for this mixer.
-  AudioParameters output_params_;
+  const scoped_refptr<AudioRendererSink> audio_sink_;
 
   // ---------------[ All variables below protected by |lock_| ]---------------
   base::Lock lock_;
 
   // List of error callbacks used by this mixer.
   typedef std::list<base::Closure> ErrorCallbackList;
   ErrorCallbackList error_callbacks_;
 
   // Each of these converters mixes inputs with a given sample rate and
   // resamples them to the output sample rate. Inputs not reqiuring resampling
   // go directly to |master_converter_|.
   AudioConvertersMap converters_;
 
   // Master converter which mixes all the outputs from |converters_| as well as
   // mixer inputs that are in the output sample rate.
   AudioConverter master_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_