| /* |
| * Copyright (c) 2016, 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. |
| */ |
| |
| /* |
| * @test |
| * @bug 8161720 |
| * @modules java.base/jdk.internal.misc |
| * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -Xbatch -XX:-TieredCompilation UnsafeSmallOffsetBooleanAccessTest |
| * @run main/othervm -Xbatch UnsafeSmallOffsetBooleanAccessTest |
| */ |
| |
| import java.util.Random; |
| import jdk.internal.misc.Unsafe; |
| |
| public class UnsafeSmallOffsetBooleanAccessTest { |
| static final Unsafe UNSAFE = Unsafe.getUnsafe(); |
| static final long F_OFFSET; |
| static final Random random = new Random(); |
| |
| static { |
| try { |
| F_OFFSET = UNSAFE.objectFieldOffset(T.class.getDeclaredField("f")); |
| System.out.println("The offset is: " + F_OFFSET); |
| } catch (Exception e) { |
| throw new Error(e); |
| } |
| } |
| |
| static class T { |
| boolean f; |
| } |
| |
| // Always return false in a way that is not obvious to the compiler. |
| public static boolean myRandom() { |
| if (random.nextInt(101) > 134) { |
| return true; |
| } else { |
| return false; |
| } |
| } |
| |
| public static boolean test(T t) { |
| boolean result = false; |
| for (int i = 0; i < 20000; i++) { |
| boolean random = myRandom(); |
| // If myRandom() returns false, access t.f. |
| // |
| // If myRandom() returns true, access virtual address |
| // F_OFFSET. That address is most likely not mapped, |
| // therefore the access will most likely cause a |
| // crash. We're not concerned about that, though, because |
| // myRandom() always returns false. However, the C2 |
| // compiler avoids normalization of the value returned by |
| // getBoolean in this case. |
| result = UNSAFE.getBoolean(myRandom() ? null : t, F_OFFSET); |
| } |
| return result; |
| } |
| |
| public static void main(String[] args) { |
| T t = new T(); |
| UNSAFE.putBoolean(t, F_OFFSET, true); |
| System.out.println("The result for t is: " + test(t)); |
| } |
| } |