/*

 * Copyright 1999 Sun Microsystems, Inc.  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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 */

/* @test

 * @bug 4178693

 * @summary Ensure that null queue arguments don't crash the Reference handler

 * @author Mark Reinhold

 */

import java.lang.ref.Reference;

import java.lang.ref.WeakReference;

public class NullQueue {

    private static Reference r = null;

    private static Thread findThread(String name) {

        /* Find reference-handler thread */

        ThreadGroup tg = Thread.currentThread().getThreadGroup();

        for (ThreadGroup tgn = tg;

             tgn != null;

             tg = tgn, tgn = tg.getParent());

        int nt = tg.activeCount();

        Thread[] ts = new Thread[nt];

        tg.enumerate(ts);

        Thread refHandler = null;

        for (int i = 0; i < ts.length; i++) {

            if (ts[i].getName().equals(name)) return ts[i];

        }

        return null;

    }

    private static void fork(Runnable proc) throws InterruptedException {

        Thread t = new Thread(proc);

        t.start();

        t.join();

    }

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

        Thread refHandler = findThread("Reference Handler");

        if (refHandler == null)

            throw new Exception("Couldn't find Reference-handler thread");

        if (!refHandler.isAlive())

            throw new Exception("Reference-handler thread is not alive");

        /* Invoke a Reference constructor, passing null for the queue */

        fork(new Runnable() {

            public void run() {

                r = new WeakReference(new Object(), null);

            }});

        /* Force the reference to be cleared and enqueued by the GC */

        for (int i = 0;; i++) {

            Thread.sleep(10);

            System.gc();

            if (r.get() == null) break;

            if (i >= 10)

                throw new Exception("Couldn't cause weak ref to be cleared");

        }

        /* Check that the handler is still alive */

        if (!refHandler.isAlive())

            throw new Exception("Reference-handler thread died");

    }

}