8193445: JavaFX CSS is applied redundantly leading to significant performance degradation

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

@@ -9415,6 +9415,13 @@ final void reapplyCSS() {
 
         if (cssFlag == CssFlags.REAPPLY) return;
 
+        if (cssFlag == CssFlags.DIRTY_BRANCH) {
+            // JDK-8193445 - don't reapply CSS from here
+            // Defer CSS application to this Node by marking cssFlag as REAPPLY
+            cssFlag = CssFlags.REAPPLY;
+            return;
+        }
+
         // RT-36838 - don't reapply CSS in the middle of an update
         if (cssFlag == CssFlags.UPDATE) {
             cssFlag = CssFlags.REAPPLY;

tests/system/src/test/java/test/javafx/scene/QuadraticCssTimeTest.java

@@ -0,0 +1,125 @@
+/*
+ * Copyright (c) 2019, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package test.javafx.scene;
+
+import javafx.application.Application;
+import javafx.application.Platform;
+import javafx.geometry.Insets;
+import javafx.scene.Scene;
+import javafx.scene.layout.HBox;
+import javafx.scene.layout.BorderPane;
+import javafx.scene.text.Text;
+import javafx.stage.Stage;
+import javafx.stage.WindowEvent;
+
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+import test.util.Util;
+import junit.framework.Assert;
+import org.junit.Test;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * This test is based on the test case reported in JDK-8209830
+ *
+ * Redundant CSS Re-application was avoided in JDK-8193445.
+ * It results in faster application of CSS on Controls (Nodes). In turn,
+ * resulting in improved Node creation/addition time to a Scene.
+ *
+ * The goal of this test is *NOT* to measure absolute performance, but to show
+ * creating and adding 500 Nodes to a scene does not take more than a
+ * particular threshold of time.
+ *
+ * The selected thresold is larger than actual observed time.
+ * It is not a benchmark value. It is good enough to catch the regression
+ * in performance, if any.
+ */
+
+public class QuadraticCssTimeTest {
+
+    private static CountDownLatch startupLatch;
+    private static Stage stage;
+    private static BorderPane rootPane;
+
+    public static class TestApp extends Application {
+
+        @Override
+        public void start(Stage primaryStage) throws Exception {
+            stage = primaryStage;
+            rootPane = new BorderPane();
+            stage.setScene(new Scene(rootPane));
+            stage.addEventHandler(WindowEvent.WINDOW_SHOWN, e -> {
+                Platform.runLater(() -> startupLatch.countDown());
+            });
+            stage.show();
+        }
+    }
+
+    @BeforeClass
+    public static void initFX() throws Exception {
+        startupLatch = new CountDownLatch(1);
+        new Thread(() -> Application.launch(QuadraticCssTimeTest.TestApp.class, (String[]) null)).start();
+
+        assertTrue("Timeout waiting for FX runtime to start", startupLatch.await(15, TimeUnit.SECONDS));
+    }
+
+    @Test
+    public void testTimeForAdding500NodesToScene() throws Exception {
+
+        Util.runAndWait(() -> {
+            // Compute time for adding 500 Nodes
+            long startTime = System.currentTimeMillis();
+
+            HBox hbox = new HBox();
+            for (int i = 0; i < 500; i++) {
+                hbox = new HBox(new Text("y"), hbox);
+                final HBox h = hbox;
+                h.setPadding(new Insets(1));
+            }
+            rootPane.setCenter(hbox);
+
+            long endTime = System.currentTimeMillis();
+
+            System.out.println("Time to create and add 500 nodes to a Scene = " +
+                               (endTime - startTime) + " mSec");
+
+            // NOTE : 800 mSec is not a benchmark value
+            // It is good enough to catch the regression in performance, if any
+            assertTrue("Time to add 500 Nodes is more than 800 mSec", (endTime - startTime) < 800);
+        });
+    }
+
+    @AfterClass
+    public static void teardownOnce() {
+        Platform.runLater(() -> {
+            stage.hide();
+            Platform.exit();
+        });
+    }
+}