Switching MediaStreamManager from using AudioManager to AudioSystem

media/audio/audio_system.h

 // Copyright 2017 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 MEDIA_AUDIO_AUDIO_SYSTEM_H_
 #define MEDIA_AUDIO_AUDIO_SYSTEM_H_
 
 #include "base/callback.h"
 #include "media/base/audio_parameters.h"
 #include "media/base/media_export.h"
 
+namespace base {
+class SingleThreadTaskRunner;
+}
+
 namespace media {
 class AudioManager;
 
 // Work in progress: Provides asynchronous interface to AudioManager. All the
 // AudioManager clients will be switched to it, in preparation for moving
 // to Mojo audio service.
 class MEDIA_EXPORT AudioSystem {
  public:
-  // Replies are asynchronously sent to the thread the call is issued on.
+  // Replies are asynchronously sent from audio system thread to the thread the
+  // call is issued on. Attention! Since audio system thread may outlive all the
+  // others, callbacks must always be bound to weak pointers!
   using OnAudioParamsCallback = base::Callback<void(const AudioParameters&)>;
   using OnBoolCallback = base::Callback<void(bool)>;
 
   static AudioSystem* Get();
 
   virtual ~AudioSystem();
 
   // Callback may receive invalid parameters, it means the specified device is
   // not found. This is best-effort: valid parameters do not guarantee existance
   // of the device.
   // TODO(olka,tommi): fix all AudioManager implementations to return invalid
   // parameters if the device is not found.
   virtual void GetInputStreamParameters(
       const std::string& device_id,
       OnAudioParamsCallback on_params_cb) const = 0;
 
   // If media::AudioDeviceDescription::IsDefaultDevice(device_id) is true,
   // callback will receive the parameters of the default output device.
   // Callback may receive invalid parameters, it means the specified device is
   // not found. This is best-effort: valid parameters do not guarantee existance
   // of the device.
   // TODO(olka,tommi): fix all AudioManager implementations to return invalid
   // parameters if the device is not found.
   virtual void GetOutputStreamParameters(
       const std::string& device_id,
       OnAudioParamsCallback on_params_cb) const = 0;
 
   virtual void HasInputDevices(OnBoolCallback on_has_devices_cb) const = 0;
 
+  virtual base::SingleThreadTaskRunner* GetTaskRunner() const = 0;
+
   // Must not be used for anything but stream creation.
   virtual AudioManager* GetAudioManager() const = 0;
 
  protected:
   // Sets the global AudioSystem pointer to the specified non-null value.
   static void SetInstance(AudioSystem* audio_system);
 
   // Sets the global AudioSystem pointer to null if it equals the specified one.
   static void ClearInstance(const AudioSystem* audio_system);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_SYSTEM_H_