Add reference counter of DxgiDuplicatorController to unload DXGI components

webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h

Index: webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h
diff --git a/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h b/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h
index c9838ad7a1e5d63c918da9b22fcde0c0276d0dac..67c58aa24354506e9b67402dcbc01715e96a0999 100644
--- a/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h
+++ b/webrtc/modules/desktop_capture/win/dxgi_duplicator_controller.h
@@ -13,6 +13,7 @@
 
 #include <D3DCommon.h>
 
+#include <atomic>
 #include <memory>
 #include <vector>
 
@@ -39,8 +40,15 @@ namespace webrtc {
 // changing. Consumers should retry after a while. (Typically 50 milliseconds,
 // but according to hardware performance, this time may vary.)
 class DxgiDuplicatorController {
+ private:
+  struct ReferenceReleaser final {
+    void operator()(DxgiDuplicatorController* instance) const;
+  };
+
  public:
   using Context = DxgiFrameContext;
+  using Reference =
+      std::unique_ptr<DxgiDuplicatorController, ReferenceReleaser>;

[Do not use (sergeyu), 2017/06/15 19:25:19]

Do we really need this instead of scoped_refptr<>?

[Hzj_jie, 2017/06/15 20:32:02]

I can imagine three solutions by using scoped_refptr.
1. scoped_refptr<DxgiDuplicatorController>, while DxgiDuplicatorController
inherits rtc::RefCountedObject.
That seems not right: there is at most one DxgiDuplicatorController instance, so
deleting this singleton instance or creating another one are both not right.

2. scoped_refptr<DxgiDuplicatorControllerUnloader>. In the destructor of
DxgiDuplicatorControllerUnloader, we will call the Unload() function.
The problem is that consumers need to access DxgiDuplicatorController from
DxgiDuplicatorControllerUnloader, i.e. DxgiDuplicatorControllerUnloader needs to
have operator-> or operator*, which has been implemented by std::unique_ptr
already.

3. scoped_refptr<DxgiDuplicatorController>, and let DxgiDuplicatorController
implement rtc::RefCountInterface itself.
I have not seen a significant difference, except for the ReferenceReleaser
functor. (I need to write several more lines of code.)

If you are talking about the third solution, I have no objective to use it. But
I prefer stl over scoped_refptr.

[Sergey Ulanov, 2017/06/16 05:59:58]

I was thinking about (3), but I think (1) may work as well if you keep the
constructor private and make the destructor reset a global reference kept
internally (i.e. you always have either 0 or 1 instance of the class). 
The problem with the current solution is that unique_ptr<> is used for an object
that is not owned. It looks to the consumer as if it gets its own instance of
the controller, which is not true. Also scoped_refptr<> is the common solution
for any ref-counted object, so it seems to make sense to use it here.

Another alternative that I would prefer over the current solution is to have
Reference as a class with a move semantics similar to unique_ptr<>. 

 
   // A collection of D3d information we are interested on, which may impact
   // capturer performance or reliability.
@@ -65,14 +73,11 @@ class DxgiDuplicatorController {
     INVALID_MONITOR_ID,
   };
 
+  // Deprecated: use "GetRefence()" instead.
   // Returns the singleton instance of DxgiDuplicatorController.
   static DxgiDuplicatorController* Instance();
 
-  // Destructs current instance. We need to make sure COM components and their
-  // containers are destructed in correct order. This function calls
-  // Deinitialize() to do the real work.
-  ~DxgiDuplicatorController();
-
+  static Reference GetReference();
   // All the following public functions implicitly call Initialize() function.
 
   // Detects whether the system supports DXGI based capturer.
@@ -108,15 +113,23 @@ class DxgiDuplicatorController {
   friend DxgiFrameContext::~DxgiFrameContext();
 
   // A private constructor to ensure consumers to use
-  // DxgiDuplicatorController::Instance().
+  // DxgiDuplicatorController::GetReference().
   DxgiDuplicatorController();
 
+  // Not implemented: The singleton DxgiDuplicatorController instance should not
+  // be deleted.
+  ~DxgiDuplicatorController();
+
   // Does the real duplication work. Setting |monitor_id| < 0 to capture entire
   // screen. This function calls Initialize(). And if the duplication failed,
   // this function calls Deinitialize() to ensure the Dxgi components can be
   // reinitialized next time.
   Result DoDuplicate(DxgiFrame* frame, int monitor_id);
 
+  // Unload all the DXGI components and releases the resources. This function
+  // wraps Deinitialize() with |lock_|.
+  void Unload();
+
   // Unregisters Context from this instance and all DxgiAdapterDuplicator(s)
   // it owns.
   void Unregister(const Context* const context);
@@ -185,6 +198,9 @@ class DxgiDuplicatorController {
   // DxgiAdapterDuplicator and DxgiOutputDuplicator instances are initialized.
   void TranslateRect();
 
+  // The count of references which are now "living".
+  static std::atomic_int refcount_;
+
   // This lock must be locked whenever accessing any of the following objects.
   rtc::CriticalSection lock_;