1 /*
   2  * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
  23 
  24 /*
  25  * @test
  26  * @summary Test that hidden classes get garbage collected.
  27  * @library /test/lib
  28  * @modules jdk.compiler
  29  * @run main GCHiddenClass
  30  */
  31 
  32 
  33 import java.lang.invoke.MethodType;
  34 import java.lang.invoke.MethodHandles;
  35 import java.lang.invoke.MethodHandles.Lookup;
  36 import java.lang.ref.PhantomReference;
  37 import java.lang.ref.Reference;
  38 import java.lang.ref.ReferenceQueue;
  39 
  40 import static java.lang.invoke.MethodHandles.Lookup.ClassOption.*;
  41 import jdk.test.lib.compiler.InMemoryJavaCompiler;
  42 
  43 // This test is based on test vmTestbase/vm/mlvm/anonloader/func/isGarbageCollected/Test.java
  44 public class GCHiddenClass {
  45 
  46     static byte klassbuf[] = InMemoryJavaCompiler.compile("TestClass",
  47         "public class TestClass { " +
  48         "    public TestClass() { " +
  49         "        System.out.println(\"Hello\"); " +
  50         " } } ");
  51 
  52     // A private method is great to keep hidden Class reference local to make it
  53     // GCed on the next cycle
  54     private PhantomReference<Class<?>> createClass(ReferenceQueue<Class<?>> refQueue) throws Exception {
  55         Lookup lookup = MethodHandles.lookup();
  56         Class<?> cl = lookup.defineHiddenClass(klassbuf, false, NESTMATE).lookupClass();
  57         return new PhantomReference<Class<?>>(cl, refQueue);
  58     }
  59 
  60     public boolean run() throws Exception {
  61         ReferenceQueue<Class<?>> refQueue = new ReferenceQueue<Class<?>>();
  62         PhantomReference<Class<?>> hiddenClassRef = createClass(refQueue);
  63         System.gc();
  64         Reference<? extends Class<?>> deletedObject = refQueue.remove();
  65         return hiddenClassRef.equals(deletedObject);
  66     }
  67 
  68     public static void main(String[] args) throws Throwable {
  69         GCHiddenClass gcHC = new GCHiddenClass();
  70         if (!gcHC.run()) {
  71             throw new RuntimeException("Test failed");
  72         }
  73     }
  74 }