Caching AudioOutputDevice instances in mixer manager

content/renderer/media/audio_renderer_sink_cache_impl.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_IMPL_H_
+#define CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_SINK_CACHE_IMPL_H_
+
+#include "content/renderer/media/audio_renderer_sink_cache.h"
+
+#include <vector>
+
+#include "base/single_thread_task_runner.h"
+#include "base/synchronization/lock.h"
+#include "base/time/time.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+// AudioRendererSinkCache implementation.
+class CONTENT_EXPORT AudioRendererSinkCacheImpl
+    : public AudioRendererSinkCache {
+ public:
+  // Callback to be used for AudioRendererSink creation
+  using CreateSinkCallback =
+      base::Callback<scoped_refptr<media::AudioRendererSink>(
+          int render_frame_id,
+          int session_id,
+          const std::string& device_id,
+          const url::Origin& security_origin)>;
+
+  AudioRendererSinkCacheImpl(
+      scoped_refptr<base::SingleThreadTaskRunner> task_runner,
+      const CreateSinkCallback& create_sink_callback,
+      const base::TimeDelta delete_timeout);
+
+  ~AudioRendererSinkCacheImpl() final;
+
+  media::OutputDeviceInfo GetSinkInfo(int source_render_frame_id,
+                                      int session_id,
+                                      const std::string& device_id,
+                                      const url::Origin& security_origin) final;
+
+  scoped_refptr<media::AudioRendererSink> GetSink(
+      int source_render_frame_id,
+      const std::string& device_id,
+      const url::Origin& security_origin) final;
+
+  void ReleaseSink(const media::AudioRendererSink* sink_ptr) final;
+
+ private:
+  friend class AudioRendererSinkCacheTest;
+  friend class CacheEntryFinder;
+
+  struct CacheEntry;
+  using CacheContainer = std::vector<CacheEntry>;
+
+  // Schedules a sink for deletion. Deletion will be performed on the same
+  // thread the cache is created on.
+  void DeleteLaterIfUnused(const media::AudioRendererSink* sink_ptr);
+
+  // Deletes a sink from the cache. If |force_delete_used| is set, a sink being
+  // deleted can (and should) be in use at the moment of deletion; otherwise the
+  // sink is deleted only if unused.
+  void DeleteSink(const media::AudioRendererSink* sink_ptr,
+                  bool force_delete_used);
+
+  CacheContainer::iterator FindCacheEntry_Locked(
+      int source_render_frame_id,
+      const std::string& device_id,
+      const url::Origin& security_origin,
+      bool unused_only);
+
+  int GetCacheSizeForTesting();
+
+  // Task runner for scheduled sink garbage collection.
+  const scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  // Callback used for sink creation.
+  const CreateSinkCallback create_sink_cb_;
+
+  // Cached sink deletion timeout.
+  // For example: (1) sink was created and cached in GetSinkInfo(), and then (2)
+  // the same sink is requested in GetSink(), if time interval between (1) and
+  // (2) is less than |kDeleteTimeoutMs|, then sink cached in (1) is reused in
+  // (2). On the other hand, if after (1) nobody is interested in the sink
+  // within |kDeleteTimeoutMs|, it is garbage-collected.
+  const base::TimeDelta delete_timeout_;
+
+  // Cached sinks, protected by lock.
+  base::Lock cache_lock_;
+  CacheContainer cache_;
+
+  // Weak pointer to be used for delayed sink deletion on |task_runner_|.
+  // Pre-created in constructor and is used to post all the delayed tasks.
+  // A delayed task can be concurrently posted from any thread the cache is used
+  // on, so on-the-flight weak pointer creation with
+  // weak_ptr_factory_.GetWeakPtr() can't be used, because it will result in the
+  // racy access to the factory.

[o1ka, 2016/05/26 09:00:27]

Another alternative would be to post the task under cache_lock_ as it was done
initially. (If I understand the code correctly, weak_factory is bound to a
thread on WeakPtr dereference/invalidation only.)

+  base::WeakPtr<AudioRendererSinkCacheImpl> weak_this_;
+
+  // Used to produce |weak_this_| on AudioRendererSinkCacheImpl construction.
+  base::WeakPtrFactory<AudioRendererSinkCacheImpl> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioRendererSinkCacheImpl);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_RENDERER_MEDIA_AUDIO_RENDERER_SINK_CACHE_IMPL_H_