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 "base/memory/weak_ptr.h"

[miu, 2016/05/12 21:53:06]

This include doesn't seem to be used.

[o1ka, 2016/05/17 17:17:24]

Done.

+#include "content/common/content_export.h"
+#include "media/base/output_device_info.h"
+#include "url/origin.h"

[miu, 2016/05/12 21:53:06]

nit: Chromium code takes the opposite stance from the Google C++ style guide in
that url::Origin should just be forward-declared, rather than its header file
#included. (Then, #include the header in the .cc file.)

[o1ka, 2016/05/17 17:17:24]

Done.

+
+namespace media {
+class AudioRendererSink;
+}
+
+namespace content {
+
+// Caches AudioRendererSink instances (owns them), provides them to the clients
+// for usage, tracks their used/unused state, garbage-collects unused sinks.
+// Thread safe.
+class CONTENT_EXPORT AudioRendererSinkCache {

[miu, 2016/05/12 21:53:06]

naming nit: This feels more like a "pool" than a "cache" since this class is
managing the lifecycle [including delayed deletion] of the ARS objects.

[o1ka, 2016/05/17 17:17:24]

Now it does not quite manage the lifetime any more. I also thought of it as a
cache in terms of hits/misses when getting a sink/OutputDeviceInfo

+ public:
+  // Creates default cache, to be used by AudioRendererMixerManager.
+  static std::unique_ptr<AudioRendererSinkCache> CreateDefault();
+
+  // 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(). Does not pass sink ownership; sink is guaranteed to
+  // be alive until ReleaseSink().
+  virtual media::AudioRendererSink* GetSink(
+      int source_render_frame_id,
+      const std::string& device_id,
+      const url::Origin& security_origin) = 0;
+
+  // Returns the sink to the chache when it's not needed any more. Must be
+  // called by the client, so that the cache can garbage-collect the sink.
+  virtual void ReleaseSink(media::AudioRendererSink* sink) = 0;
+
+  virtual ~AudioRendererSinkCache() {}
+
+ protected:
+  AudioRendererSinkCache() {}
+
+  DISALLOW_COPY_AND_ASSIGN(AudioRendererSinkCache);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_SINK_CACHE_H_