Refactor video capturing code in the render process

content/renderer/media/video_capture_impl_manager.h

 // Copyright (c) 2012 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.
 
-// VideoCaptureImplManager owns VideoCaptureImpl objects. Clients who
-// want access to a video capture device call UseDevice() to get a handle
-// to VideoCaptureImpl.
+// TODO(hclam): This class should be renamed to VideoCaptureService.
+
+// This class provides access to a video capture device in the browser
+// process through IPC. The main function is to deliver video frames
+// to a client.
 //
 // THREADING
 //
 // VideoCaptureImplManager lives only on the render thread. All methods
 // must be called on this thread.
 //
-// The handle returned by UseDevice() is thread-safe. It ensures
-// destruction is handled on the render thread.
+// VideoFrames are delivered on the IO thread. Callbacks provided by
+// a client are also called on the IO thread.
+//
+// LIFETIME
+//
+// This class is refcounted but not thread-safe. This allows cleanup of
+// video capture resources after all clients are destroyed.

[Ami GONE FROM CHROMIUM, 2014/04/21 23:42:53]

Is it possible to use WeakPtrs to avoid letting clients keep this class longer
than desired?

In the absence of this I worry about RTI giving up its ref, but this VCIM
outliving RTI and bad things happening.

[Alpha Left Google, 2014/04/23 18:48:33]

Good point. Done.

 
 #ifndef CONTENT_RENDERER_MEDIA_VIDEO_CAPTURE_IMPL_MANAGER_H_
 #define CONTENT_RENDERER_MEDIA_VIDEO_CAPTURE_IMPL_MANAGER_H_
 
 #include <map>
 
 #include "base/callback.h"
 #include "base/memory/linked_ptr.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_checker.h"
 #include "content/common/content_export.h"
-#include "media/video/capture/video_capture.h"
+#include "content/common/media/video_capture.h"
+#include "media/video/capture/video_capture_types.h"
 
 namespace content {
 
 class VideoCaptureImpl;
-class VideoCaptureImplManager;
 class VideoCaptureMessageFilter;
 
-// Thread-safe wrapper for a media::VideoCapture object. During
-// destruction |destruction_cb| is called. This mechanism is used
-// by VideoCaptureImplManager to ensure de-initialization and
-// destruction of the media::VideoCapture object happens on the render
-// thread.
-class CONTENT_EXPORT VideoCaptureHandle : media::VideoCapture {
- public:
-  virtual ~VideoCaptureHandle();
-
-  // media::VideoCapture implementations.
-  virtual void StartCapture(
-      EventHandler* handler,
-      const media::VideoCaptureParams& params) OVERRIDE;
-  virtual void StopCapture(EventHandler* handler) OVERRIDE;
-  virtual bool CaptureStarted() OVERRIDE;
-  virtual int CaptureFrameRate() OVERRIDE;
-  virtual void GetDeviceSupportedFormats(
-      const DeviceFormatsCallback& callback) OVERRIDE;
-  virtual void GetDeviceFormatsInUse(
-      const DeviceFormatsInUseCallback& callback) OVERRIDE;
-
- private:
-  friend class VideoCaptureImplManager;
-
-  VideoCaptureHandle(media::VideoCapture* impl,
-                     base::Closure destruction_cb);
-
-  media::VideoCapture* impl_;
-  base::Closure destruction_cb_;
-
-  DISALLOW_COPY_AND_ASSIGN(VideoCaptureHandle);
-};
-
-class CONTENT_EXPORT VideoCaptureImplManager {
+class CONTENT_EXPORT VideoCaptureImplManager :
+      public base::RefCounted<VideoCaptureImplManager> {
  public:
   VideoCaptureImplManager();
-  virtual ~VideoCaptureImplManager();
 
-  // Returns a video capture device referenced by |id|.
-  scoped_ptr<VideoCaptureHandle> UseDevice(media::VideoCaptureSessionId id);
+  // Access a device associated with the session ID.

[Ami GONE FROM CHROMIUM, 2014/04/21 23:42:53]

s/Access/Open/
(or Use or something else more active)

[Alpha Left Google, 2014/04/23 18:48:33]

Done.

+  // This method must be called before any methods with the same ID
+  // is used.
+  // Returns a callback that is used to release the acquired resources.

[Ami GONE FROM CHROMIUM, 2014/04/21 23:42:53]

s/is/should be/

[Alpha Left Google, 2014/04/23 18:48:33]

Done.

+  base::Closure UseDevice(media::VideoCaptureSessionId id);
+
+  // Start receiving video frames for the given session ID.
+  //
+  // |state_update_cb| will be called on the IO thread when capturing
+  // state changes.
+  // States will be one of the following four:
+  // * VIDEO_CAPTURE_STATE_STARTED
+  // * VIDEO_CAPTURE_STATE_STOPPED
+  // * VIDEO_CAPTURE_STATE_PAUSED
+  // * VIDEO_CAPTURE_STATE_ERROR
+  //
+  // |deliver_frame_cb| will be called on the IO thread when a video
+  // frame is ready.
+  //
+  // Returns a callback that is used to stop capturing. Note that stopping
+  // video capture is not synchronous. Client should handle the case where
+  // callbacks are called after capturing is instructed to stop.

[Ami GONE FROM CHROMIUM, 2014/04/21 23:42:53]

s/./, typically by binding the passed callbacks on a WeakPtr./

[Alpha Left Google, 2014/04/23 18:48:33]

Done.

+  base::Closure StartCapture(
+      media::VideoCaptureSessionId id,
+      const media::VideoCaptureParams& params,
+      const VideoCaptureStateUpdateCB& state_update_cb,
+      const VideoCaptureDeliverFrameCB& deliver_frame_cb);
+
+  // Get supported formats by the device for the given session ID.

[Ami GONE FROM CHROMIUM, 2014/04/21 23:42:53]

Get formats supported by the device...

[Alpha Left Google, 2014/04/23 18:48:33]

Done.

+  // |callback| will be called on the IO thread.
+  void GetDeviceSupportedFormats(
+      media::VideoCaptureSessionId id,
+      const VideoCaptureDeviceFormatsCB& callback);
+
+  // Get supported formats currently in use for the given session ID.
+  // |callback| will be called on the IO thread.
+  void GetDeviceFormatsInUse(
+      media::VideoCaptureSessionId id,
+      const VideoCaptureDeviceFormatsCB& callback);
 
   // Make all existing VideoCaptureImpl instances stop/resume delivering
   // video frames to their clients, depends on flag |suspend|.
   void SuspendDevices(bool suspend);
 
   VideoCaptureMessageFilter* video_capture_message_filter() const {
     return filter_.get();
   }
 
  protected:
-  // Used in tests to inject a mock VideoCaptureImpl.
+  friend class base::RefCounted<VideoCaptureImplManager>;
+  virtual ~VideoCaptureImplManager();
   virtual VideoCaptureImpl* CreateVideoCaptureImpl(

[Ami GONE FROM CHROMIUM, 2014/04/21 23:42:53]

s/Impl(/ImplForTesting(/

[Alpha Left Google, 2014/04/23 18:48:33]

Done.

       media::VideoCaptureSessionId id,
       VideoCaptureMessageFilter* filter) const;
 
  private:
+  void StopCapture(int client_id, media::VideoCaptureSessionId id);
   void UnrefDevice(media::VideoCaptureSessionId id);
 
   // The int is used to count clients of the corresponding VideoCaptureImpl.
+  // VideoCaptureImpl objects are owned by this object. But they are
+  // destroyed on the IO thread. These are raw pointers because we destroy
+  // them manually.
   typedef std::map<media::VideoCaptureSessionId,
-                   std::pair<int, linked_ptr<VideoCaptureImpl> > >
+                   std::pair<int, VideoCaptureImpl*> >
       VideoCaptureDeviceMap;
   VideoCaptureDeviceMap devices_;
 
+  // This is an internal ID for identifying clients of VideoCaptureImpl.
+  // The ID is global for the render process.
+  int next_client_id_;
+
   scoped_refptr<VideoCaptureMessageFilter> filter_;
 
   // Bound to the render thread.
   base::ThreadChecker thread_checker_;
 
   // Bound to the render thread.
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<VideoCaptureImplManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoCaptureImplManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_VIDEO_CAPTURE_IMPL_MANAGER_H_