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 java.compiler
  29  *          java.management
  30  * @run main GCHiddenClass
  31  */
  32 
  33 
  34 import java.lang.invoke.MethodType;
  35 import java.lang.invoke.MethodHandles;
  36 import java.lang.invoke.MethodHandles.Lookup;
  37 import java.lang.ref.PhantomReference;
  38 import java.lang.ref.Reference;
  39 import java.lang.ref.ReferenceQueue;
  40 
  41 import static java.lang.invoke.MethodHandles.Lookup.ClassOption.*;
  42 import jdk.test.lib.compiler.InMemoryJavaCompiler;
  43 
  44 // This test is based on test vmTestbase/vm/mlvm/anonloader/func/isGarbageCollected/Test.java
  45 public class GCHiddenClass {
  46 
  47     static byte klassbuf[] = InMemoryJavaCompiler.compile("TestClass",
  48         "public class TestClass { " +
  49         "    public TestClass() { " +
  50         "        System.out.println(\"Hello\"); " +
  51         " } } ");
  52 
  53     // A private method is great to keep hidden Class reference local to make it
  54     // GCed on the next cycle
  55     private PhantomReference<Class<?>> createClass(ReferenceQueue<Class<?>> refQueue) throws Exception {
  56         Lookup lookup = MethodHandles.lookup();
  57         Class<?> cl = lookup.defineHiddenClass(klassbuf, false, NESTMATE, WEAK).lookupClass();
  58         return new PhantomReference<Class<?>>(cl, refQueue);
  59     }
  60 
  61     public boolean run() throws Exception {
  62         ReferenceQueue<Class<?>> refQueue = new ReferenceQueue<Class<?>>();
  63         PhantomReference<Class<?>> hiddenClassRef = createClass(refQueue);
  64         System.gc();
  65         Reference<? extends Class<?>> deletedObject = refQueue.remove();
  66         return hiddenClassRef.equals(deletedObject);
  67     }
  68 
  69     public static void main(String[] args) throws Throwable {
  70         GCHiddenClass gcHC = new GCHiddenClass();
  71         if (!gcHC.run()) {
  72             throw new RuntimeException("Test failed");
  73         }
  74     }
  75 }