Caching AudioOutputDevice instances in mixer manager

content/renderer/media/audio_renderer_sink_cache.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 CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_SINK_CACHE_H_
+#define CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_SINK_CACHE_H_
+
+#include <string>
+
+#include "content/common/content_export.h"
+#include "media/base/output_device_info.h"
+
+namespace url {
+class Origin;
+}
+
+namespace media {
+class AudioRendererSink;
+}
+
+namespace content {
+
+// Caches AudioRendererSink instances, provides them to the clients for usage,
+// tracks their used/unused state, reuses them to obtain output device
+// information, garbage-collects unused sinks.
+// Thread safe.
+class CONTENT_EXPORT AudioRendererSinkCache {
+ public:
+  virtual ~AudioRendererSinkCache() {}
+
+  // Creates default cache, to be used by AudioRendererMixerManager.
+  static std::unique_ptr<AudioRendererSinkCache> Create();
+
+  // Returnes output device information for a specified sink.

[Guido Urdaneta, 2016/05/25 13:33:13]

typo: s/Returnes/Returns

[o1ka, 2016/05/25 14:52:11]

Done.

+  virtual media::OutputDeviceInfo GetSinkInfo(
+      int source_render_frame_id,
+      int session_id,
+      const std::string& device_id,
+      const url::Origin& security_origin) = 0;
+
+  // Provides a sink for usage. The sink must be returned to the cache by
+  // calling ReleaseSink(). The sink must be stopped by the user before
+  // deletion, but after releasing it from the cache.

[Guido Urdaneta, 2016/05/25 13:33:13]

How come? Why not stop it before releasing it from the cache?

[o1ka, 2016/05/25 14:52:11]

(discussed offline - review comment is obsolete)

+  virtual scoped_refptr<media::AudioRendererSink> GetSink(
+      int source_render_frame_id,
+      const std::string& device_id,
+      const url::Origin& security_origin) = 0;
+
+  // Notifies the cache that the sink is not in use any more. Must be
+  // called by the client, so that the cache can garbage-collect the sink
+  // reference.
+  virtual void ReleaseSink(const media::AudioRendererSink* sink_ptr) = 0;
+
+ protected:
+  AudioRendererSinkCache() {}
+
+  DISALLOW_COPY_AND_ASSIGN(AudioRendererSinkCache);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_SINK_CACHE_H_