[Mojo Video Capture] Simplify media::VideoCaptureDevice::Client:Buffer to a struct

media/capture/video/video_capture_device.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.
 //
 // VideoCaptureDevice is the abstract base class for realizing video capture
 // device support in Chromium. It provides the interface for OS dependent
 // implementations.
 // The class is created and functions are invoked on a thread owned by
 // VideoCaptureManager. Capturing is done on other threads, depending on the OS
 // specific implementation.
@@ skipping 12 matching lines @@
 #include "base/files/file.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "media/base/video_frame.h"
 #include "media/capture/capture_export.h"
 #include "media/capture/mojo/image_capture.mojom.h"
 #include "media/capture/video/scoped_result_callback.h"
+#include "media/capture/video/video_capture_buffer_handle.h"
 #include "media/capture/video/video_capture_device_descriptor.h"
 #include "media/capture/video_capture_types.h"
 #include "mojo/public/cpp/bindings/array.h"
 #include "ui/gfx/gpu_memory_buffer.h"
 
 namespace tracked_objects {
 class Location;
 }  // namespace tracked_objects
 
 namespace media {
 
 class CAPTURE_EXPORT FrameBufferPool {
  public:
   virtual ~FrameBufferPool() {}
 
   virtual void SetBufferHold(int buffer_id) = 0;
   virtual void ReleaseBufferHold(int buffer_id) = 0;
-  virtual mojo::ScopedSharedBufferHandle GetHandleForTransit(int buffer_id) = 0;
 };
 
 class CAPTURE_EXPORT VideoFrameConsumerFeedbackObserver {
  public:
   virtual ~VideoFrameConsumerFeedbackObserver() {}
 
   // During processing of a video frame, consumers may report back their
   // utilization level to the source device. The device may use this information
   // to adjust the rate of data it pushes out. Values are interpreted as
   // follows:
@@ skipping 19 matching lines @@
 class CAPTURE_EXPORT VideoCaptureDevice
     : public VideoFrameConsumerFeedbackObserver {
  public:
 
   // Interface defining the methods that clients of VideoCapture must have. It
   // is actually two-in-one: clients may implement OnIncomingCapturedData() or
   // ReserveOutputBuffer() + OnIncomingCapturedVideoFrame(), or all of them.
   // All clients must implement OnError().
   class CAPTURE_EXPORT Client {
    public:
-    // Memory buffer returned by Client::ReserveOutputBuffer().
-    class CAPTURE_EXPORT Buffer {
+    // Move-only struct representing access to a buffer handle as well as
+    // read-write permission to its contents.
+    struct CAPTURE_EXPORT Buffer {

[mcasas, 2017/01/05 20:37:02]

A struct with private members and accessors and subclasses
is more a class, really -- also because |handle_provider| and
|buffer_read_write_permission| are unique_ptr<>s, so what 
is exactly happening if they're accessed (move, or access by
pointer) is not clear from the data type.  I'd vote for class and
accessors.

[chfremer, 2017/01/05 22:44:48]

Done.

      public:
-      virtual ~Buffer() = 0;
-      virtual int id() const = 0;
-      virtual int frame_feedback_id() const = 0;
-      virtual gfx::Size dimensions() const = 0;
-      virtual size_t mapped_size() const = 0;
-      virtual void* data(int plane) = 0;
-      void* data() { return data(0); }
-#if defined(OS_POSIX) && !(defined(OS_MACOSX) && !defined(OS_IOS))
-      virtual base::FileDescriptor AsPlatformFile() = 0;
-#endif
-      virtual bool IsBackedByVideoFrame() const = 0;
-      virtual scoped_refptr<VideoFrame> GetVideoFrame() = 0;
+      // Destructor-only interface for encapsulating scoped access permission to
+      // a Buffer.
+      class CAPTURE_EXPORT ScopedAccessPermission {
+       public:
+        virtual ~ScopedAccessPermission() {}
+      };
+
+      class CAPTURE_EXPORT HandleProvider {
+       public:
+        virtual ~HandleProvider() {}
+        virtual mojo::ScopedSharedBufferHandle
+        GetHandleForInterProcessTransit() = 0;
+        virtual std::unique_ptr<VideoCaptureBufferHandle>
+        GetHandleForInProcessAccess() = 0;
+      };
+
+      Buffer();
+      Buffer(
+          int buffer_id,
+          int frame_feedback_id,
+          std::unique_ptr<HandleProvider> handle_provider,
+          std::unique_ptr<ScopedAccessPermission> buffer_read_write_permission);

[mcasas, 2017/01/05 20:37:02]

s/buffer_read_write_permission/access_permission/ ?
Also the member.

[chfremer, 2017/01/05 22:44:48]

Done.

+      ~Buffer();
+      Buffer(Buffer&& other);
+      Buffer& operator=(Buffer&& other);
+
+      bool is_valid() const { return handle_provider != nullptr; }
+      int id() const { return id_; }
+      int frame_feedback_id() const { return frame_feedback_id_; }
+
+      std::unique_ptr<HandleProvider> handle_provider;
+      std::unique_ptr<ScopedAccessPermission> buffer_read_write_permission;
+
+     private:
+      int id_;
+      int frame_feedback_id_;
     };

[mcasas, 2017/01/05 20:37:02]

I think that to make Buffer uncopyable, we have to add
here
DISALLOW_COPY_AND_ASSIGN(Buffer)

to explicitly delete the "normal" copy and assign ctors, right?

https://cs.chromium.org/chromium/src/base/macros.h?q=DISALLOW_COPY&sq=package...

[chfremer, 2017/01/05 22:44:48]

Well, no. It seems that by providing a move constructor and move assignment
operator, we are implicitly deleting the copy and assign ctors. The compiler
says "error: call to implicitly-deleted copy constructor" when trying to use the
copy constructor.
Even if it didn't implicitly delete, the std::unique_ptr<> members would raise a
compile-time error when attempting a copy operation (only with a maybe less
direct error message).

Since there is not much cost to the extra line of code, I guess making it
explicit is probably better.

Done.

 
     virtual ~Client() {}
 
     // Captured a new video frame, data for which is pointed to by |data|.
     //
     // The format of the frame is described by |frame_format|, and is assumed to
     // be tightly packed. This method will try to reserve an output buffer and
     // copy from |data| into the output buffer. If no output buffer is
     // available, the frame will be silently dropped. |reference_time| is
     // system clock time when we detect the capture happens, it is used for
@@ skipping 16 matching lines @@
                                         int frame_feedback_id = 0) = 0;
 
     // Reserve an output buffer into which contents can be captured directly.
     // The returned Buffer will always be allocated with a memory size suitable
     // for holding a packed video frame with pixels of |format| format, of
     // |dimensions| frame dimensions. It is permissible for |dimensions| to be
     // zero; in which case the returned Buffer does not guarantee memory
     // backing, but functions as a reservation for external input for the
     // purposes of buffer throttling.
     //
-    // The output buffer stays reserved and mapped for use until the Buffer
-    // object is destroyed or returned.
-    virtual std::unique_ptr<Buffer> ReserveOutputBuffer(
-        const gfx::Size& dimensions,
-        VideoPixelFormat format,
-        VideoPixelStorage storage,
-        int frame_feedback_id) = 0;
+    // The buffer stays reserved for use by the caller as long as it
+    // holds on to the contained |buffer_read_write_permission|.
+    virtual Buffer ReserveOutputBuffer(const gfx::Size& dimensions,
+                                       VideoPixelFormat format,
+                                       VideoPixelStorage storage,
+                                       int frame_feedback_id) = 0;
 
     // Provides VCD::Client with a populated Buffer containing the content of
     // the next video frame. The |buffer| must originate from an earlier call to
     // ReserveOutputBuffer().
     // See OnIncomingCapturedData for details of |reference_time| and
     // |timestamp|.
-    virtual void OnIncomingCapturedBuffer(std::unique_ptr<Buffer> buffer,
+    virtual void OnIncomingCapturedBuffer(Buffer buffer,
                                           const VideoCaptureFormat& format,
                                           base::TimeTicks reference_time,
                                           base::TimeDelta timestamp) = 0;
 
     // Extended version of OnIncomingCapturedBuffer() allowing clients to
     // pass a custom |visible_rect| and |additional_metadata|.
     virtual void OnIncomingCapturedBufferExt(
-        std::unique_ptr<Buffer> buffer,
+        Buffer buffer,
         const VideoCaptureFormat& format,
         base::TimeTicks reference_time,
         base::TimeDelta timestamp,
         gfx::Rect visible_rect,
         const VideoFrameMetadata& additional_metadata) = 0;
 
     // Attempts to reserve the same Buffer provided in the last call to one of
     // the OnIncomingCapturedBufferXXX() methods. This will fail if the content
     // of the Buffer has not been preserved, or if the |dimensions|, |format|,
     // or |storage| disagree with how it was reserved via ReserveOutputBuffer().
     // When this operation fails, nullptr will be returned.
-    virtual std::unique_ptr<Buffer> ResurrectLastOutputBuffer(
-        const gfx::Size& dimensions,
-        VideoPixelFormat format,
-        VideoPixelStorage storage,
-        int new_frame_feedback_id) = 0;
+    virtual Buffer ResurrectLastOutputBuffer(const gfx::Size& dimensions,
+                                             VideoPixelFormat format,
+                                             VideoPixelStorage storage,
+                                             int new_frame_feedback_id) = 0;
 
     // An error has occurred that cannot be handled and VideoCaptureDevice must
     // be StopAndDeAllocate()-ed. |reason| is a text description of the error.
     virtual void OnError(const tracked_objects::Location& from_here,
                          const std::string& reason) = 0;
 
     // VideoCaptureDevice requests the |message| to be logged.
     virtual void OnLog(const std::string& message) {}
 
     // Returns the current buffer pool utilization, in the range 0.0 (no buffers
@@ skipping 87 matching lines @@
 
  private:
   // Gets the power line frequency from the current system time zone if this is
   // defined, otherwise returns 0.
   PowerLineFrequency GetPowerLineFrequencyForLocation() const;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_CAPTURE_VIDEO_VIDEO_CAPTURE_DEVICE_H_