investigating memory error in runtime shutdown

src/dlangui/platforms/common/platform.d

@@ -479,6 +479,8 @@ class Window {
 class Platform {
     static __gshared Platform _instance;
     static void setInstance(Platform instance) {
+        if (_instance)
+            destroy(_instance);
         _instance = instance;
     }
     @property static Platform instance() {

src/dlangui/platforms/sdl/sdlapp.d

@@ -17,6 +17,7 @@ version(USE_SDL) {
 	import dlangui.graphics.ftfonts;
 	import dlangui.graphics.resources;
 	import dlangui.widgets.styles;
+	import dlangui.widgets.widget;
 	import dlangui.platforms.common.platform;
 
 	import derelict.sdl2.sdl;
@@ -123,6 +124,7 @@ version(USE_SDL) {
 		}
 
 		void redraw() {
+            Log.e("Widget instance count in SDLWindow.redraw: ", Widget.instanceCount());
             // check if size has been changed
             int w, h;
             SDL_GetWindowSize(_win,
@@ -748,16 +750,25 @@ version(USE_SDL) {
         int res = 0;
 
         res = UIAppMain(args);
+        //Log.e("Widget instance count after UIAppMain: ", Widget.instanceCount());
 
-        Platform.setInstance(null);
         Log.d("Destroying SDL platform");
-        destroy(sdl);
+        Platform.setInstance(null);
+
+        //
+        debug {
+            Widget.shuttingDown();
+        }
 
         currentTheme = null;
         drawableCache = null;
         imageCache = null;
         FontManager.instance = null;
-
+        debug {
+            if (Widget.instanceCount() > 0) {
+                Log.e("Non-zero Widget instance count when exiting: ", Widget.instanceCount());
+            }
+        }
         Log.d("Exiting main");
 
         return res;

src/dlangui/widgets/lists.d

@@ -62,6 +62,9 @@ class WidgetListAdapter : ListAdapter {
 	override uint resetItemState(int index, uint flags) {
 		return _widgets.get(index).resetState(flags).state;
 	}
+    ~this() {
+        //Log.d("Destroying WidgetListAdapter");
+    }
 }
 
 /// List
@@ -348,6 +351,7 @@ class ListWidget : WidgetGroup, OnScrollHandler {
 	}
 
     ~this() {
+        //Log.d("Destroying List ", _id);
         if (_adapter !is null && _ownAdapter)
             destroy(_adapter);
         _adapter = null;

src/dlangui/widgets/widget.d

@@ -121,19 +121,39 @@ class Widget {
     /// set new trackHover flag value (when true, widget will change Hover state while mouse is moving)
     @property Widget trackHover(bool v) { _trackHover = v; return this; }
 
-	//private static int _instanceCount = 0;
+    debug {
+	    private static int _instanceCount = 0;
+        private static bool _appShuttingDown = false;
+    }
 	/// create widget, with optional id
     this(string ID = null) {
 		_id = ID;
         _state = State.Enabled;
+        debug {
+            _instanceCount++;
+        }
 		//Log.d("Created widget, count = ", ++_instanceCount);
     }
 	~this() {
+        debug {
+            //Log.v("destroying widget ", _id);
+            if (_appShuttingDown)
+                Log.e("Destroying widget ", _id, " after app shutdown: probably, resource leak");
+            _instanceCount--;
+        }
 		if (_ownStyle !is null)
 			destroy(_ownStyle);
 		_ownStyle = null;
 		//Log.d("Destroyed widget, count = ", --_instanceCount);
 	}
+    debug {
+        /// for debug purposes - number of created widget objects, not yet destroyed
+        static @property int instanceCount() { return _instanceCount; }
+        /// for debug purposes - sets shutdown flag to log widgets not destroyed in time.
+        static void shuttingDown() {
+            _appShuttingDown = true;
+        }
+    }
 
     /// accessor to style - by lookup in theme by styleId (if style id is not set, theme base style will be used).
 	protected @property const (Style) style() const {