Caching AudioOutputDevice instances in mixer manager

media/base/audio_renderer_mixer_pool.h

+// Copyright 2016 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_POOL_H_
+#define MEDIA_BASE_AUDIO_RENDERER_MIXER_POOL_H_
+
+#include <string>
+
+#include "media/base/output_device_info.h"
+
+namespace url {
+class Origin;
+}
+
+namespace media {
+class AudioParameters;
+class AudioRendererMixer;
+
+class MEDIA_EXPORT AudioRendererMixerPool {
+ public:
+  AudioRendererMixerPool() {}
+  virtual ~AudioRendererMixerPool() {}
+
+  // Obtains a pointer to mixer instance based on AudioParameters. The pointer
+  // is guaranteed to be valid (at least) until it's rereleased by a call to
+  // ReturnMixer()
+  virtual AudioRendererMixer* GetMixer(int source_render_frame_id,
+                                       const AudioParameters& params,
+                                       const std::string& device_id,
+                                       const url::Origin& security_origin,
+                                       OutputDeviceStatus* device_status) = 0;
+
+  // Returns mixer back to the pool.
+  virtual void ReturnMixer(int source_render_frame_id,

[miu, 2016/05/19 22:27:16]

Are all these arguments necessary to return a mixer? Could the client instead
just provide the pointer? Meaning:

  AudioRendererMixer* mixer = pool->GetMixer(...);
  ...use mixer...
  pool->ReturnMixer(mixer);
  mixer = nullptr;

[o1ka, 2016/05/20 10:40:32]

Those are the key used to look-up the mixer. Just a pointer can be used as well,
but this is how it was originally done and I don't think it makes sense to
change it in this CL (and I'm not sure it's beneficial overall
performance-wise).

+                           const AudioParameters& params,
+                           const std::string& device_id,
+                           const url::Origin& security_origin) = 0;
+
+  // Returns output device information
+  virtual OutputDeviceInfo GetOutputDeviceInfo(
+      int source_render_frame_id,
+      int session_id,
+      const std::string& device_id,
+      const url::Origin& security_origin) = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(AudioRendererMixerPool);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_AUDIO_RENDERER_MIXER_POOL_H_