/*

 * Copyright (c) 2013, 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.io.File;

import java.io.FileInputStream;

import java.io.InputStream;

import java.lang.instrument.ClassDefinition;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

/**

 * When an exception is thrown, the JVM collects just enough information

 * about the stack trace to be able to create a full fledged stack trace

 * (StackTraceElement[]). The backtrace contains this information and the

 * JVM  must make sure that the data in the backtrace is still usable after

 * a class redefinition.

 *

 * After the PermGen removal there was a bug when the last reference to a Method

 * was in the backtrace. The class of the method was kept alive, because of the

 * mirror stored in the backtrace, but the old versions of the redefined method

 * could be freed, since class redefinition didn't know about the backtraces.

 */

public class RedefineMethodInBacktraceApp {

    public static void main(String args[]) throws Exception {

        System.out.println("Hello from RedefineMethodInBacktraceApp!");

        new RedefineMethodInBacktraceApp().doTest();

        System.exit(0);

    }

    private void doTest() throws Exception {

        doMethodInBacktraceTest();

    }

    private void doMethodInBacktraceTest() throws Exception {

        Throwable t = getThrowableFromMethodToRedefine();

        doRedefine(RedefineMethodInBacktraceTarget.class);

        doClassUnloading();

        touchRedefinedMethodInBacktrace(t);

    }

    private static Throwable getThrowableFromMethodToRedefine() throws Exception {

        Class<RedefineMethodInBacktraceTarget> c =

                RedefineMethodInBacktraceTarget.class;

        Method method = c.getMethod("methodToRedefine");

        Throwable thrownFromMethodToRedefine = null;

        try {

            method.invoke(null);

        } catch (InvocationTargetException e) {

            thrownFromMethodToRedefine = e.getCause();

            if (!(thrownFromMethodToRedefine instanceof RuntimeException)) {

                throw e;

            }

        }

        method = null;

        c = null;

        return thrownFromMethodToRedefine;

    }

    private static void doClassUnloading() {

        // This will clean out old, unused redefined methods.

        System.gc();

    }

    private static void touchRedefinedMethodInBacktrace(Throwable throwable) {

        // Make sure that we can convert the backtrace, which is referring to

        // the redefined method, to a  StrackTraceElement[] without crashing.

        throwable.getStackTrace();

    }

    private static void doRedefine(Class<?> clazz) throws Exception {

        // Load the second version of this class.

        File f = new File(clazz.getName() + ".class");

        System.out.println("Reading test class from " + f.getAbsolutePath());

        InputStream redefineStream = new FileInputStream(f);

        byte[] redefineBuffer = NamedBuffer.loadBufferFromStream(redefineStream);

        ClassDefinition redefineParamBlock = new ClassDefinition(

                clazz, redefineBuffer);

        RedefineMethodInBacktraceAgent.getInstrumentation().redefineClasses(

                new ClassDefinition[] {redefineParamBlock});

    }

}