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:
+  // Creates default cache, to be used by AudioRendererMixerManager.
+  static std::unique_ptr<AudioRendererSinkCache> Create();
+
+  // Returnes output device information for a specified sink.
+  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().
+  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(int source_render_frame_id,
+                           const std::string& device_id,
+                           const url::Origin& security_origin,
+                           const media::AudioRendererSink* sink) = 0;
+
+  virtual ~AudioRendererSinkCache() {}

[miu, 2016/05/19 22:27:15]

style nit: dtors are usually near the top. This one should probably go  after
the Create() function decl.

[o1ka, 2016/05/23 16:16:54]

I check with the style guide, and it should be the first, before any methods,
including static ones.

+
+ protected:
+  AudioRendererSinkCache() {}
+
+  DISALLOW_COPY_AND_ASSIGN(AudioRendererSinkCache);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_SINK_CACHE_H_