jdk

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/*
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 * Copyright (c) 2020, 2021, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 */
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/*
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 * @test
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 * @summary Test that hidden classes get garbage collected.
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 * @library /test/lib
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 * @modules jdk.compiler
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 * @run main GCHiddenClass
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 */
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import java.lang.invoke.MethodType;
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import java.lang.invoke.MethodHandles;
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import java.lang.invoke.MethodHandles.Lookup;
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import java.lang.ref.PhantomReference;
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import java.lang.ref.Reference;
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import java.lang.ref.ReferenceQueue;
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import static java.lang.invoke.MethodHandles.Lookup.ClassOption.*;
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import jdk.test.lib.compiler.InMemoryJavaCompiler;
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public class GCHiddenClass {
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    static byte klassbuf[] = InMemoryJavaCompiler.compile("TestClass",
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        "public class TestClass { " +
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        "    public TestClass() { " +
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        "        System.out.println(\"Hello\"); " +
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        " } } ");
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    // A private method is great to keep hidden Class reference local to make it
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    // GCed on the next cycle
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    private PhantomReference<Class<?>> createClass(ReferenceQueue<Class<?>> refQueue) throws Exception {
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        Lookup lookup = MethodHandles.lookup();
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        Class<?> cl = lookup.defineHiddenClass(klassbuf, false, NESTMATE).lookupClass();
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        return new PhantomReference<Class<?>>(cl, refQueue);
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    }
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    public boolean run() throws Exception {
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        ReferenceQueue<Class<?>> refQueue = new ReferenceQueue<Class<?>>();
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        PhantomReference<Class<?>> hiddenClassRef = createClass(refQueue);
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        System.gc();
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        Reference<? extends Class<?>> deletedObject = refQueue.remove();
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        return hiddenClassRef.equals(deletedObject);
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    }
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    public static void main(String[] args) throws Throwable {
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        GCHiddenClass gcHC = new GCHiddenClass();
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        if (!gcHC.run()) {
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            throw new RuntimeException("Test failed");
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        }
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    }
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}
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