cc: Various code safety improvements in video compositing code.

cc/layers/video_frame_provider_client_impl.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 CC_LAYERS_VIDEO_FRAME_PROVIDER_CLIENT_IMPL_H_
 #define CC_LAYERS_VIDEO_FRAME_PROVIDER_CLIENT_IMPL_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_checker.h"
+#include "cc/base/cc_export.h"
 #include "cc/layers/video_frame_provider.h"
 #include "ui/gfx/transform.h"
 
-namespace media { class VideoFrame; }
+namespace media {
+class VideoFrame;
+}  // namespace media

[danakj, 2015/03/24 17:38:01]

(this isn't actually needed by the linter for small forward declare blocks)

[sunnyps, 2015/03/24 19:43:38]

Done.

 
 namespace cc {
+

[danakj, 2015/03/24 17:38:01]

why whitespace?

[sunnyps, 2015/03/24 19:43:38]

Done.

 class VideoLayerImpl;
 
-class VideoFrameProviderClientImpl
+// VideoFrameProviderClientImpl liasons with the VideoFrameProvider and the
+// VideoLayer. It receives updates from the provider and updates the layer as a
+// result. It also allows the layer to access the video frame that the provider
+// has.
+class CC_EXPORT VideoFrameProviderClientImpl
     : public VideoFrameProvider::Client,
       public base::RefCounted<VideoFrameProviderClientImpl> {
  public:
+  // Must be created on the impl thread while the main thread is blocked.
   static scoped_refptr<VideoFrameProviderClientImpl> Create(
       VideoFrameProvider* provider);
 
-  VideoLayerImpl* active_video_layer() { return active_video_layer_; }
-  void SetActiveVideoLayer(VideoLayerImpl* video_layer);
+  // Must be called on the impl thread.
+  void Start(VideoLayerImpl* active_video_layer);
+  bool Started() const;
+  bool Stopped() const;
 
+  // Must be called on the impl thread while the main thread is blocked. It is
+  // legal to call Stop without calling Start.
   void Stop();
-  bool Stopped();
 
   scoped_refptr<media::VideoFrame> AcquireLockAndCurrentFrame();
   void PutCurrentFrame(const scoped_refptr<media::VideoFrame>& frame);
   void ReleaseLock();
   const gfx::Transform& stream_texture_matrix() const {
     return stream_texture_matrix_;
   }
 
-  // VideoFrameProvider::Client implementation. These methods are all callable
-  // on any thread.
+  // VideoFrameProvider::Client implementation.
+  // Called on the main thread.
   void StopUsingProvider() override;
+  // Called on the impl thread.
   void DidReceiveFrame() override;
   void DidUpdateMatrix(const float* matrix) override;
 
  private:
-  explicit VideoFrameProviderClientImpl(VideoFrameProvider* provider);
   friend class base::RefCounted<VideoFrameProviderClientImpl>;
+
+  VideoFrameProviderClientImpl(VideoFrameProvider* provider);
   ~VideoFrameProviderClientImpl() override;
 
+  VideoFrameProvider* provider_;
   VideoLayerImpl* active_video_layer_;
+  bool stopped_;
 
-  // Guards the destruction of provider_ and the frame that it provides
+  // Since the provider lives on another thread, it can be destroyed while the
+  // frame controller are accessing it's frame. Before being destroyed the
+  // provider calls StopUsingProvider. provider_lock_ blocks StopUsingProvider
+  // from returning till the frame controller is done using the frame.
   base::Lock provider_lock_;
-  VideoFrameProvider* provider_;
   base::ThreadChecker thread_checker_;
 
   gfx::Transform stream_texture_matrix_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoFrameProviderClientImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_VIDEO_FRAME_PROVIDER_CLIENT_IMPL_H_