8279214: Memory leak in Scene after dragging a cell

Reviewed-by: angorya, arapte

Author: Marius Hanl

modules/javafx.graphics/src/main/java/javafx/scene/Scene.java

@@ -3668,6 +3668,7 @@ private void clearPDREventTargets() {
                     ? currentEventTargets.get(0) : null;
             pdrEventTarget.clear();
             pdrEventTargets.clear();
+            fullPDRTmpTargetWrapper.clear();
         }
 
         public void enterFullPDR(EventTarget gestureSource) {

modules/javafx.graphics/src/test/java/test/javafx/scene/SceneTest.java

@@ -1030,4 +1030,45 @@ public void testAddNullPostLayoutPulseListener() {
         // Verify TilePane was GC'd:
         JMemoryBuddy.assertCollectable(ref);
     }
+
+    @Test public void testNoReferencesRemainToRemovedNodeAfterStartingFullDrag() {
+        TilePane pane = new TilePane();
+        pane.setMinSize(200, 200);
+
+        WeakReference<TilePane> ref = new WeakReference<>(pane);
+
+        Group root = new Group(pane);
+        final Scene scene = new Scene(root, 400, 400);
+        stage.setScene(scene);
+
+        pane.setOnDragDetected(event -> ((Node) event.getSource()).startFullDrag());
+
+        // Simulate a drag operation from the user
+        SceneHelper.processMouseEvent(scene,
+                MouseEventGenerator.generateMouseEvent(MouseEvent.MOUSE_PRESSED, 50, 50));
+
+        SceneHelper.processMouseEvent(scene,
+                MouseEventGenerator.generateMouseEvent(MouseEvent.MOUSE_DRAGGED, 70, 70));
+
+        SceneHelper.processMouseEvent(scene,
+                MouseEventGenerator.generateMouseEvent(MouseEvent.MOUSE_RELEASED, 50, 50));
+
+        root.getChildren().setAll(new StackPane());
+
+        // Generate a MOUSE_EXITED event for the removed node and a pulse as otherwise many unrelated Scene references
+        // hang around to the removed node:
+        SceneHelper.processMouseEvent(
+                scene,
+                new MouseEvent(
+                        MouseEvent.MOUSE_EXITED, 50, 50, 50, 50, MouseButton.NONE, 0, false, false, false,
+                        false, false, false, false, false, false, true, null
+                )
+        );
+
+        Toolkit.getToolkit().firePulse();
+
+        pane = null;
+
+        JMemoryBuddy.assertCollectable(ref);
+    }
 }