Move passing of WebRTC rendering frames to IO thread

content/renderer/media/webmediaplayer_ms.h

 // Copyright 2013 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_WEBMEDIAPLAYER_MS_H_
 #define CONTENT_RENDERER_MEDIA_WEBMEDIAPLAYER_MS_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 202 matching lines @@
 
   std::unique_ptr<MediaStreamRendererFactory> renderer_factory_;
 
   const scoped_refptr<base::SingleThreadTaskRunner> media_task_runner_;
   const scoped_refptr<base::TaskRunner> worker_task_runner_;
   media::GpuVideoAcceleratorFactories* gpu_factories_;
 
   // Used for DCHECKs to ensure methods calls executed in the correct thread.
   base::ThreadChecker thread_checker_;
 
-  // WebMediaPlayerMS owns |compositor_| and destroys it on
-  // |compositor_task_runner_|.
-  std::unique_ptr<WebMediaPlayerMSCompositor> compositor_;
+  scoped_refptr<WebMediaPlayerMSCompositor> compositor_;

[DaleCurtis, 2016/12/03 01:17:54]

Can we avoid this? 

[emircan, 2016/12/03 01:42:13]

I can think of a way of avoiding this, but I mentioned briefly in the CL
description why I preferred not to. Let me know if I am missing smt, you can
think of another way or prefer this.
I still need to post WebMediaPlayerMSCompositor::Enqueue frame on
media_task_runner. (Main and compositor are janky, and using IO all the way here
is too long of a task for IO.) If this class is not ref counted, I would need a
WeakPtr to access it. Then, I would need two WeakPtrFactory's since there is
already one in use for compositor thread here. In dtor(or earlier), I need to
make sure that both are invalidated in their respective threads. That would
require synchronization/blocking until the other is completed.

[DaleCurtis, 2016/12/06 01:00:42]

Is this true? Or would it be sufficient to just generate a cancellable callback
you can hand out?

 
   const scoped_refptr<base::SingleThreadTaskRunner> compositor_task_runner_;
 
   const std::string initial_audio_output_device_id_;
   const url::Origin initial_security_origin_;
 
   // The last volume received by setVolume() and the last volume multiplier from
   // OnVolumeMultiplierUpdate().  The multiplier is typical 1.0, but may be less
   // if the WebMediaPlayerDelegate has requested a volume reduction (ducking)
   // for a transient sound.  Playout volume is derived by volume * multiplier.
   double volume_;
   double volume_multiplier_;
 
   // True if playback should be started upon the next call to OnShown(). Only
   // used on Android.
   bool should_play_upon_shown_;
 
   DISALLOW_COPY_AND_ASSIGN(WebMediaPlayerMS);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_WEBMEDIAPLAYER_MS_H_