8064468: ownedWindowList access requires synchronization in Window.setAlwaysOnTop() method

Reviewed-by: serb, pchelko

jdk/src/java.desktop/share/classes/java/awt/Window.java

@@ -2254,7 +2254,18 @@ public class Window extends Container implements Accessible {
             }
             firePropertyChange("alwaysOnTop", oldAlwaysOnTop, alwaysOnTop);
         }
-        for (WeakReference<Window> ref : ownedWindowList) {
+        setOwnedWindowsAlwaysOnTop(alwaysOnTop);
+    }
+
+    @SuppressWarnings({"rawtypes", "unchecked"})
+    private void setOwnedWindowsAlwaysOnTop(boolean alwaysOnTop) {
+        WeakReference<Window>[] ownedWindowArray;
+        synchronized (ownedWindowList) {
+            ownedWindowArray = new WeakReference[ownedWindowList.size()];
+            ownedWindowList.copyInto(ownedWindowArray);
+        }
+
+        for (WeakReference<Window> ref : ownedWindowArray) {
             Window window = ref.get();
             if (window != null) {
                 try {

jdk/test/java/awt/Window/AlwaysOnTop/SyncAlwaysOnTopFieldTest.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2014, 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.
+ *
+ * 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.
+ */
+
+import java.awt.Window;
+
+/**
+ * @test
+ * @bug 8064468
+ * @author Alexander Scherbatiy
+ * @summary ownedWindowList access requires synchronization in
+ *     Window.setAlwaysOnTop() method
+ * @run main SyncAlwaysOnTopFieldTest
+ */
+public class SyncAlwaysOnTopFieldTest {
+
+    private static final int WINDOWS_COUNT = 200;
+    private static final int STEPS_COUNT = 20;
+
+    public static void main(String[] args) throws Exception {
+        final Window rootWindow = createWindow(null);
+
+        new Thread(() -> {
+            for (int i = 0; i < WINDOWS_COUNT; i++) {
+                createWindow(rootWindow);
+            }
+        }).start();
+
+        boolean alwaysOnTop = true;
+        for (int i = 0; i < STEPS_COUNT; i++) {
+            Thread.sleep(10);
+            rootWindow.setAlwaysOnTop(alwaysOnTop);
+            alwaysOnTop = !alwaysOnTop;
+        }
+    }
+
+    private static Window createWindow(Window parent) {
+        Window window = new Window(parent);
+        window.setSize(200, 200);
+        window.setVisible(true);
+        return window;
+    }
+}