Add support for the audio-output-device switching IPC mechanism to the renderer lower layers (media…

media/base/audio_output_device_callback_util.h

+// Copyright (c) 2015 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.
+//
+// Provides an utility class to support invocation of callbacks in the correct

[DaleCurtis, 2015/06/11 17:58:47]

Why not use media::BindToCurrentLoop?

[Guido Urdaneta, 2015/06/11 20:10:09]

Done.

+// thread for the SwitchOutputDevice operation provided by
+// media::AudioRendererSink and other related classes.
+// The rationale for this class is that SwitchOutputDevice operations go
+// through many layers (i.e., from blink to the browser and back), and
+// the request can move throughout multiple threads. It is impossible for
+// the lower layers to know the right thread where the callback should be run.
+// This class provides a convenient way for users to create callbacks that
+// can assume they will be run on the correct thread, and for implementors of
+// SwitchOutputDevice, which can easily invoke the callback without having
+// to worry about threads.
+// Note that the methods of this class can be called on any thread, but they
+// cannot be called concurrently by multiple threads.
+
+#ifndef MEDIA_BASE_AUDIO_OUTPUT_DEVICE_CALLBACK_UTIL_H_
+#define MEDIA_BASE_AUDIO_OUTPUT_DEVICE_CALLBACK_UTIL_H_
+
+#include "base/callback.h"
+#include "base/single_thread_task_runner.h"
+#include "media/audio/audio_output_ipc.h"
+
+namespace media {
+
+typedef base::Callback<void(SwitchOutputDeviceResult)>
+    SwitchOutputDeviceCallback;
+
+class MEDIA_EXPORT SwitchOutputDeviceCallbackRunner {
+ public:
+  SwitchOutputDeviceCallbackRunner(
+      scoped_ptr<SwitchOutputDeviceCallback> callback,
+      const scoped_refptr<base::SingleThreadTaskRunner>& callback_task_runner);
+
+  ~SwitchOutputDeviceCallbackRunner();
+
+  // Posts the execution of |callback_| to |callback task runner_|, and
+  // relinquishes ownership of both afterwards. |result| is passed as the
+  // argument for |callback_|.
+  // Calling this method a second time has no effect.
+  void Run(SwitchOutputDeviceResult result);
+
+ private:
+  scoped_ptr<SwitchOutputDeviceCallback> callback_;
+  scoped_refptr<base::SingleThreadTaskRunner> callback_task_runner_;
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_AUDIO_OUTPUT_DEVICE_CALLBACK_UTIL_H_