Eliminate video capture thread in renderer

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 manages video capture devices in renderer process.
-// The video capture clients use AddDevice() to get a pointer to
-// video capture device. VideoCaputreImplManager supports multiple clients
-// accessing same device.
+// VideoCaptureImplManager owns VideoCaptureImpl objects. Clients who
+// want access to a video capture device call UseDevice() to get a handle
+// to VideoCaptureImpl.
+//
+// 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.
 
 #ifndef CONTENT_RENDERER_MEDIA_VIDEO_CAPTURE_IMPL_MANAGER_H_
 #define CONTENT_RENDERER_MEDIA_VIDEO_CAPTURE_IMPL_MANAGER_H_
 
-#include <list>
 #include <map>
 
+#include "base/callback.h"
+#include "base/memory/linked_ptr.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop_proxy.h"
-#include "base/threading/thread.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"
 
 namespace content {
 
 class VideoCaptureImpl;
+class VideoCaptureImplManager;
 class VideoCaptureMessageFilter;
 
-class CONTENT_EXPORT VideoCaptureImplManager
-    : public base::RefCountedThreadSafe<VideoCaptureImplManager> {
+// Thread-safe wrapper for a media::VideoCapture object. During

[Ami GONE FROM CHROMIUM, 2014/01/08 01:43:58]

Did you notice I recommended RefCountedDeleteOnMessageLoop, not
RefCountedThreadSafe?  I think this does what you need, already (ref counting
followed by delete on a specific pre-specified thread, regardless of which
thread the last ref is released on)

[Alpha Left Google, 2014/01/08 22:30:50]

Yes I have considered your suggestion.

Currently work done when a VCI is released are: unref, VCI::DeInitOnIOThread()
and then delete. This can be done by RefCountedDeleteOnMessageLoop I think, by
calling VCI::DeInitOnIOThread() in VCI::~VCI().

However a reference to VCI must be saved in VCIM such that it can be shared to
multiple users. If VCI is RefCountedDeleteOnMessageLoop then we would a method
like VCIM::Release(VCI*) to remove this reference held by VCIM. 

+// 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 {

[Ami GONE FROM CHROMIUM, 2014/01/08 01:43:58]

Could make it a public inner class of VCIM.  Not sure it's worth it.

+ 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;
+
+ 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 {
  public:
   VideoCaptureImplManager();
+  virtual ~VideoCaptureImplManager();
 
-  // Called by video capture client |handler| to add device referenced
-  // by |id| to VideoCaptureImplManager's list of opened device list.
-  // A pointer to VideoCapture is returned to client so that client can
-  // operate on that pointer, such as StartCaptrue, StopCapture.
-  virtual media::VideoCapture* AddDevice(
-      media::VideoCaptureSessionId id,
-      media::VideoCapture::EventHandler* handler);
-
-  // Called by video capture client |handler| to remove device referenced
-  // by |id| from VideoCaptureImplManager's list of opened device list.
-  virtual void RemoveDevice(media::VideoCaptureSessionId id,
-                            media::VideoCapture::EventHandler* handler);
+  // Returns a video capture device referenced by |id|.
+  scoped_ptr<VideoCaptureHandle> UseDevice(media::VideoCaptureSessionId id);
 
   // Make all existing VideoCaptureImpl instances stop/resume delivering
   // video frames to their clients, depends on flag |suspend|.
-  virtual void SuspendDevices(bool suspend);
+  void SuspendDevices(bool suspend);
 
   VideoCaptureMessageFilter* video_capture_message_filter() const {
     return filter_.get();
   }
 
- protected:
-  virtual ~VideoCaptureImplManager();
+ private:
+  void UnrefDevice(media::VideoCaptureSessionId id);
 
- private:
-  friend class base::RefCountedThreadSafe<VideoCaptureImplManager>;
+  typedef std::map<media::VideoCaptureSessionId,
+                   std::pair<int, linked_ptr<VideoCaptureImpl> > >

[Ami GONE FROM CHROMIUM, 2014/01/08 01:43:58]

doco the int is a ref count

+      VideoCaptureDeviceMap;
+  VideoCaptureDeviceMap devices_;
 
-  struct Device {
-    Device(VideoCaptureImpl* device,
-           media::VideoCapture::EventHandler* handler);
-    ~Device();
-
-    VideoCaptureImpl* vc;
-    std::list<media::VideoCapture::EventHandler*> clients;
-  };
-
-  void FreeDevice(VideoCaptureImpl* vc);
-
-  typedef std::map<media::VideoCaptureSessionId, Device*> Devices;
-  Devices devices_;
-  base::Lock lock_;
   scoped_refptr<VideoCaptureMessageFilter> filter_;
-  base::Thread thread_;
-  scoped_refptr<base::MessageLoopProxy> message_loop_proxy_;
+  base::WeakPtrFactory<VideoCaptureImplManager> weak_factory_;

[Ami GONE FROM CHROMIUM, 2014/01/08 01:43:58]

I don't see it.

[Alpha Left Google, 2014/01/08 22:30:50]

Done.

+  base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoCaptureImplManager);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_VIDEO_CAPTURE_IMPL_MANAGER_H_