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8193445: JavaFX CSS is applied redundantly leading to significant performance degradation #34

@@ -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;

// RT-36838 - don't reapply CSS in the middle of an update
if (cssFlag == CssFlags.UPDATE) {
cssFlag = CssFlags.REAPPLY;
@@ -0,0 +1,125 @@
* Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
* 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 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 {

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());

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));

public void testTimeForAdding500NodesToScene() throws Exception {

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kevinrushforth Nov 25, 2019


Adding a node to a live scene graph must be done on the JavaFX Application thread. I recommend wrapping the body of this method in a Util.runAndWait call.

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));

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);

public static void teardownOnce() {
Platform.runLater(() -> {
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