8264330: Scene MouseHandler is referencing removed nodes

Reviewed-by: kcr

build.gradle

@@ -2089,6 +2089,7 @@ project(":graphics") {
         stubCompile group: "junit", name: "junit", version: "4.8.2"
 
         antlr group: "org.antlr", name: "antlr4", version: "4.7.2", classifier: "complete"
+        testCompile project(":base").sourceSets.test.output
         compile project(':base')
     }
 

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2010, 2021, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -3633,6 +3633,7 @@ private void clearPDREventTargets() {
             currentEventTarget = currentEventTargets.size() > 0
                     ? currentEventTargets.get(0) : null;
             pdrEventTarget.clear();
+            pdrEventTargets.clear();
         }
 
         public void enterFullPDR(EventTarget gestureSource) {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2021, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -30,6 +30,7 @@
 import javafx.beans.value.ChangeListener;
 import javafx.beans.value.ObservableValue;
 import javafx.concurrent.Task;
+import javafx.scene.input.MouseButton;
 import javafx.scene.layout.StackPane;
 import javafx.scene.layout.TilePane;
 import javafx.scene.layout.VBox;
@@ -53,6 +54,7 @@
 import org.junit.Before;
 import org.junit.Test;
 
+import java.lang.ref.WeakReference;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -68,6 +70,7 @@
 import javafx.scene.Scene;
 import javafx.scene.SceneShim;
 import javafx.scene.SubScene;
+import test.util.memory.JMemoryBuddy;
 
 import static junit.framework.Assert.assertEquals;
 import static junit.framework.Assert.assertNotNull;
@@ -971,4 +974,49 @@ public void testAddNullPostLayoutPulseListener() {
         SceneShim.scenePulseListener_pulse(scene);
         assertEquals(1, counter.get());
     }
+
+    @Test public void testNoReferencesRemainToRemovedNodeAfterBeingClicked() {
+        StubToolkit toolkit = (StubToolkit) Toolkit.getToolkit();
+        TilePane pane = new TilePane();
+        VBox vbox = new VBox(pane);
+        Scene scene = new Scene(vbox, 300, 200);
+        WeakReference<TilePane> ref = new WeakReference<>(pane);
+
+        pane.setMinSize(1000, 1000);  // ensure mouse click will hit this node
+
+        stage.setScene(scene);
+
+        // Press mouse on TilePane so it gets picked up as a potential node to drag:
+        SceneHelper.processMouseEvent(
+            scene,
+            MouseEventGenerator.generateMouseEvent(MouseEvent.MOUSE_PRESSED, 100, 100)
+        );
+
+        // Release mouse on TilePane to trigger clean up code as there will be no dragging:
+        SceneHelper.processMouseEvent(
+            scene,
+            MouseEventGenerator.generateMouseEvent(MouseEvent.MOUSE_RELEASED, 100, 100)
+        );
+
+        // Remove TilePane, and replace with something else:
+        vbox.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, 100, 100, 100, 100, MouseButton.NONE, 0, false, false, false,
+                        false, false, false, false, false, false, true, null
+                )
+        );
+
+        toolkit.firePulse();
+
+        // Clear our own reference and see if the TilePane is now not referenced anywhere:
+        pane = null;
+
+        // Verify TilePane was GC'd:
+        JMemoryBuddy.assertCollectable(ref);
+    }
 }