Prototype: need to introduce an interface for the frame data feed

Since I want to segregate the code according to the domain,
several methods must be provided to the video display to conduct
a properly synchronised handover of video pixel data; by using
`Glib::Dispatcher` as base class, all aspects of feed synchronisation
can be packaged into a single connection interface, without having
to share implementation details between the video display and player.

FrOSCon26/FrOSCon.26.mm

@@ -1057,7 +1057,7 @@
 <node BACKGROUND_COLOR="#e0ceaa" COLOR="#520f69" CREATED="1783904751803" ID="ID_648202546" MODIFIED="1783904801052" TEXT="lasse mir von Claude zwei Code-Templates generieren">
 <icon BUILTIN="edit"/>
 <node CREATED="1783904765875" ID="ID_1730135150" MODIFIED="1783904774302" TEXT="die C-L&#xf6;sung mit g_idle_add()"/>
-<node BACKGROUND_COLOR="#accdc3" COLOR="#3f4015" CREATED="1783904774961" ID="ID_795180608" MODIFIED="1783984701307" STYLE="fork" TEXT="die Gtkmm-L&#xf6;sung mit dem Glib::Dispatcher">
+<node BACKGROUND_COLOR="#accdc3" COLOR="#3f4015" CREATED="1783904774961" ID="ID_795180608" MODIFIED="1784136111537" STYLE="fork" TEXT="die Gtkmm-L&#xf6;sung mit dem Glib::Dispatcher">
 <richcontent TYPE="NOTE"><html>
   <head/>
   <body>
@@ -1083,6 +1083,7 @@
 </html></richcontent>
 <edge COLOR="#808080" STYLE="bezier" WIDTH="thin"/>
 <icon BUILTIN="wizard"/>
+<icon BUILTIN="edit"/>
 </node>
 </node>
 </node>
@@ -1249,7 +1250,7 @@
 <icon BUILTIN="yes"/>
 </node>
 <node CREATED="1783956516487" ID="ID_1971249448" MODIFIED="1783956541623" TEXT="Claude schreibt mir drei Code-Snippets">
-<node CREATED="1783956542891" ID="ID_922011151" MODIFIED="1783956927430" TEXT="Setup von Uring und Timer + initiales Bef&#xfc;llen">
+<node BACKGROUND_COLOR="#accdc3" COLOR="#3f4015" CREATED="1783956542891" ID="ID_922011151" MODIFIED="1784136111537" STYLE="fork" TEXT="Setup von Uring und Timer + initiales Bef&#xfc;llen">
 <richcontent TYPE="NOTE"><html>
   <head/>
   <body>
@@ -1312,8 +1313,11 @@
     </p>
   </body>
 </html></richcontent>
+<edge COLOR="#808080" STYLE="bezier" WIDTH="thin"/>
+<icon BUILTIN="wizard"/>
+<icon BUILTIN="edit"/>
 </node>
-<node CREATED="1783956564734" ID="ID_519769608" MODIFIED="1783956917195" TEXT="Skelett der Proactor-Loop">
+<node BACKGROUND_COLOR="#accdc3" COLOR="#3f4015" CREATED="1783956564734" ID="ID_519769608" MODIFIED="1784136111536" STYLE="fork" TEXT="Skelett der Proactor-Loop">
 <richcontent TYPE="NOTE"><html>
   <head/>
   <body>
@@ -1355,15 +1359,41 @@
     </p>
   </body>
 </html></richcontent>
+<edge COLOR="#808080" STYLE="bezier" WIDTH="thin"/>
+<icon BUILTIN="wizard"/>
+<icon BUILTIN="edit"/>
 </node>
-<node CREATED="1783956594083" ID="ID_1956714359" MODIFIED="1783956898511" TEXT="onTick + follow-up">
+<node BACKGROUND_COLOR="#accdc3" COLOR="#3f4015" CREATED="1783956594083" ID="ID_1956714359" MODIFIED="1784136509799" STYLE="fork" TEXT="onTick + follow-up">
 <richcontent TYPE="NOTE"><html>
-  <head/>
+  <head>
+    
+  </head>
   <body>
-    void onTick() { if (slots[nextExpected % N].state == Ready) { frameReady.emit(); // GUI thread will draw slots[nextExpected % N] ++nextExpected; // GUI marks the slot Empty once it's done drawing } // else: do nothing &#8212; this frame slips one tick later. Not dropped, just delayed. while (slots[nextToSubmit % N].state == Empty) { submitRead(nextToSubmit); // io_uring_prep_read + set_data64(nextToSubmit) ++nextToSubmit; } io_uring_submit(&amp;ring); }
+    <pre>void onTick()
+&#160;&#160;{
+&#160;&#160;&#160;&#160;if (slots[nextExpected % N].state == Ready)
+&#160;&#160;&#160;&#160;&#160;&#160;{
+&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;frameReady.emit(); // GUI thread will draw slots[nextExpected % N]
+&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;++nextExpected; // GUI marks the slot Empty once it's done drawing
+&#160;&#160;&#160;&#160;&#160;&#160;}
+ &#160;// else: do nothing &#8212; this frame slips one tick later. Not dropped, just delayed.
+
+  while (slots[nextToSubmit % N].state == Empty)
+  &#160;&#160;{
+&#160;&#160;  &#160;&#160;submitRead(nextToSubmit); // io_uring_prep_read + set_data64(nextToSubmit)
+     ++nextToSubmit;
+&#160;&#160;  }
+  io_uring_submit(&amp;ring);
+}
+      
+    </pre>
   </body>
-</html></richcontent>
+</html>
-<node CREATED="1783956613435" ID="ID_121998302" MODIFIED="1783956875196" TEXT="Claude erl&#xe4;utert dazu....">
+</richcontent>
+<edge COLOR="#808080" STYLE="bezier" WIDTH="thin"/>
+<icon BUILTIN="wizard"/>
+<icon BUILTIN="edit"/>
+<node CREATED="1783956613435" ID="ID_121998302" MODIFIED="1784136083060" TEXT="Claude erl&#xe4;utert dazu....">
 <richcontent TYPE="NOTE"><html>
   <head/>
   <body>
@@ -1376,7 +1406,7 @@
 </node>
 </node>
 </node>
-<node BACKGROUND_COLOR="#accdc3" COLOR="#3f4015" CREATED="1783957483612" ID="ID_918051178" MODIFIED="1783957589661" STYLE="fork" TEXT="a Zuckerl: Chrono-to-Kernel-Timespec">
+<node BACKGROUND_COLOR="#accdc3" COLOR="#3f4015" CREATED="1783957483612" ID="ID_918051178" MODIFIED="1784136111534" STYLE="fork" TEXT="a Zuckerl: Chrono-to-Kernel-Timespec">
 <richcontent TYPE="NOTE"><html>
   <head/>
   <body>
@@ -1435,6 +1465,7 @@
 </html></richcontent>
 <edge COLOR="#808080" STYLE="bezier" WIDTH="thin"/>
 <icon BUILTIN="wizard"/>
+<icon BUILTIN="edit"/>
 </node>
 <node BACKGROUND_COLOR="#e9c7a3" COLOR="#440099" CREATED="1783964845540" ID="ID_784995591" MODIFIED="1783964898453" TEXT="schlie&#xdf;e eine allgemeine &#xdc;berlegung an btr. Lumiera-Engine">
 <icon BUILTIN="back"/>
@@ -2056,7 +2087,7 @@
 <node CREATED="1784082547951" ID="ID_1261536746" MODIFIED="1784082582921" TEXT="ist ein std::array aus 8bit-Pixeln"/>
 <node COLOR="#5b280f" CREATED="1784082595689" ID="ID_1135557355" MODIFIED="1784132191641" TEXT="verwende diese Typedef aber auch als &#xbb;Buffer&#xab;-Abstraktion">
 <icon BUILTIN="stop-sign"/>
-<node CREATED="1784132084657" ID="ID_845039951" MODIFIED="1784132129048" TEXT="hier beginnt der Knoten">
+<node CREATED="1784132084657" HGAP="24" ID="ID_845039951" MODIFIED="1784132637445" TEXT="hier beginnt der Knoten" VSHIFT="7">
 <arrowlink COLOR="#b92b54" DESTINATION="ID_1404935910" ENDARROW="Default" ENDINCLINATION="101;8;" ID="Arrow_ID_1619759457" STARTARROW="None" STARTINCLINATION="53;82;"/>
 <icon BUILTIN="broken-line"/>
 </node>
@@ -2100,6 +2131,21 @@
 <node CREATED="1784131484193" ID="ID_169121010" MODIFIED="1784131533952" TEXT="Zugriff als Funktion darstellen &#x27f9; &#x3bb;">
 <linktarget COLOR="#5a94d9" DESTINATION="ID_169121010" ENDARROW="Default" ENDINCLINATION="135;0;" ID="Arrow_ID_84801803" SOURCE="ID_1267317279" STARTARROW="None" STARTINCLINATION="76;6;"/>
 </node>
+<node CREATED="1784136965047" ID="ID_1744030854" MODIFIED="1784137036831" TEXT="zu kurz gedacht: es ist eine Zugriffs-Klammer">
+<richcontent TYPE="NOTE"><html>
+  <head>
+    
+  </head>
+  <body>
+    <p>
+      Eine Operation zum Zugriff und eine Operation um den abgeschlossenen Zugriff zu markieren; zudem gibt es auch noch den Dispatcher.
+    </p>
+  </body>
+</html>
+</richcontent>
+<icon BUILTIN="messagebox_warning"/>
+</node>
+<node CREATED="1784137038242" ID="ID_1199476075" MODIFIED="1784137051164" TEXT="dann doch ein klassisches OO-Callback-Interface"/>
 </node>
 </node>
 </node>

FrOSCon26/examples/commons.hpp

@@ -29,5 +29,17 @@ __FAIL (string msg)
   std::abort();
 }
 
+/**
+ * Marker class: any copy and copy construction prohibited
+ */
+class NonCopyable
+  {
+  protected:
+   ~NonCopyable()                               = default;
+    NonCopyable()                               = default;
+    NonCopyable (NonCopyable const&)            = delete;
+    NonCopyable& operator= (NonCopyable const&) = delete;
+  };
+
 
 #endif /*COMMONS_H*/

FrOSCon26/examples/demo-uring.cpp

@@ -17,8 +17,10 @@
 #include <iostream>
 #include <memory>
 #include <thread>
+#include <atomic>
 
 using std::unique_ptr;
+using std::make_unique;
 
 //-----------------hard-coded-config--
 const size_t RING_SIZ = 5;
@@ -29,56 +31,105 @@ const uint VIDEO_HEIGHT = 240;
 
 
 class UringVideoPlayer
+  : NonCopyable
   {
     using VideoDisplay = EglDisplay<uint8_t, VIDEO_WIDTH,VIDEO_HEIGHT>;
     using Buffer = VideoDisplay::Buffer;
 
-    Glib::Dispatcher dispatchFrame_;
+    enum BuffState { FREE, READ, SHOW };
+    using AtomicBuffState = std::atomic<BuffState>;
+
+    using BufferAlloc    = unique_ptr<Buffer[]>;
+    using BuffStateAlloc = unique_ptr<AtomicBuffState[]>;
+
+    /**
+     * Connector to the VideoDisplay for dispatching video data.
+     * @note inherits from Glib::Dispatcher -> signal frame readiness
+     * @remark the callback functions allow the VideoDisplay to interact
+     *       with the buffer data and state in a threadsafe manner
+     */
+    class BufferDispatcher
+      : public VideoDisplay::PixelFeed
+      {
+        Buffer* retrieveFrame() override;
+        void completedFrame()   override;
+
+        UringVideoPlayer& player_;
+      public:
+        BufferDispatcher (UringVideoPlayer& player)
+          : player_{player}
+          { }
+      };
+
+    size_t nextRead_{0};
+    size_t nextShow_{0};
+    BufferAlloc buffer_{};
+    BuffStateAlloc buffState_{};
+    std::atomic_bool playing_{false};
+    BufferDispatcher dispatchFrame_;
     VideoDisplay  videoDisplayer_;
     std::thread proactorThread_;
 
   public:
     UringVideoPlayer (Gtk::Window& appWindow)
-      : videoDisplayer_{appWindow, dispatchFrame_, [this]{ return retrieveCurrFrame(); }}
+      : dispatchFrame_{*this}
+      , videoDisplayer_{appWindow, dispatchFrame_}
       , proactorThread_{[this]{ playVideo(); }}
       { }
 
     void terminate();
 
   private:
-    void
+    void playVideo();
-    playVideo()
+  };
-      {
+
-        // allocate buffer data structure
+
+/**
+ * Logic of the »Proactor Thread«:
+ * - maintain the working buffers
+ * - open the raw video file to retrieve data
+ * - establish an IO_URING connection for reading
+ * - periodic processing to fill and hand-off buffers
+ */
+void
+UringVideoPlayer::playVideo()
+{
+  buffer_    = make_unique<Buffer[]> (RING_SIZ);
+  buffState_ = make_unique<AtomicBuffState[]> (RING_SIZ);
   // initialise URing
   // ++ proactor-loop ++
-      }
+}
 
-    Buffer*
+
-    retrieveCurrFrame()
+UringVideoPlayer::Buffer*
-      {
+UringVideoPlayer::BufferDispatcher::retrieveFrame()
+{
   ///////OOO threadsafe hand-over of current frame data
-      }
+}
-  };
+
+
+void
+UringVideoPlayer::BufferDispatcher::completedFrame()
+{
+  ///////OOO mark end of buffer access
+}
+
+
+void
+UringVideoPlayer::terminate()
+{
+  playing_.store (false, std::memory_order_release);
+  proactorThread_.join();
+  videoDisplayer_.cleanUp();
+}
+
 
 
 unique_ptr<UringVideoPlayer>
 launchPlayer (Gtk::Window& appWindow)
 {
   appWindow.resize (VIDEO_WIDTH, VIDEO_HEIGHT);
-
+  return std::make_unique<UringVideoPlayer> (appWindow);
-  auto player = std::make_unique<UringVideoPlayer> (appWindow);
-
-  return player;
-}
-
-
-
-void
-UringVideoPlayer::terminate()
-{
-  ///// signal stop to proactor
-  videoDisplayer_.cleanUp();
 }
 
 

FrOSCon26/examples/egl-display.hpp

@@ -38,20 +38,35 @@ using std::string;
  */
 template<typename PIX, uint WIDTH, uint HEIGHT>
 class EglDisplay
+  : NonCopyable
   {
 
   public:
     using Buffer = std::array<PIX, WIDTH*HEIGHT * 3 >;
-    using PixFeed = std::function<Buffer*()>;
 
-    EglDisplay(Gtk::Window& appWindow
+    /**
-              ,Glib::Dispatcher& dispatchFrame
+     * Interface retrieve pixel data for video frames to display.
-              ,PixFeed frameCallback
+     * - this is a Glib::Dispatcher, and the attached slot shall be
-              )
+     *   triggered whenever data for a new frame is available
-      : retrieveFrame_{frameCallback}
+     * - pixel data is accessed (threadsafe) by invoking #retrieveFrame()
+     * - when processing is complete and the data will no longer be needed,
+     *   access to the pixel buffer is yielded by invoking #completedFrame()
+     */
+    class PixelFeed
+      : public Glib::Dispatcher
+      {
+      public:
+        virtual ~PixelFeed() { }; ///< this is an interface
+        virtual Buffer* retrieveFrame() =0;
+        virtual void completedFrame()   =0;
+      };
+
+
+    EglDisplay (Gtk::Window& appWindow, PixelFeed& pixelFeed)
+      : pixelFeed_{pixelFeed}
       {
         openDisplay (appWindow);
-        dispatchFrame.connect([this]{ displayFrame(); });
+        pixelFeed_.connect([this]{ displayFrame(); });
       }
 
     void cleanUp();
@@ -71,7 +86,7 @@ class EglDisplay
     float scaleY_{1};
 
     /** Callback functor to access current pixel data */
-    PixFeed retrieveFrame_{};
+    PixelFeed& pixelFeed_{};
 
     void openDisplay (Gtk::Window&);
     void displayFrame();
@@ -321,7 +336,7 @@ void
 EglDisplay<PIX,WIDTH,HEIGHT>::displayFrame()
 {
 
-  auto currFrame = retrieveFrame_();
+  auto currFrame = pixelFeed_.retrieveFrame();
   if (not currFrame) return;
 
   // pick up current buffer with RGB data
@@ -340,6 +355,9 @@ EglDisplay<PIX,WIDTH,HEIGHT>::displayFrame()
 
   // double-buffer flip, automatically invokes glFlush()
   eglSwapBuffers (display_, surface_);
+
+  // signal that processing of this frame is complete
+  pixelFeed_.completedFrame();
 }