1 /*

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

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

    21  * have any questions.

    22  */

    23 

    24 /* @test

    25  * @bug 4178693

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

    27  * @author Mark Reinhold

    28  */

    29 

    30 import java.lang.ref.Reference;

    31 import java.lang.ref.WeakReference;

    32 

    33 

    34 public class NullQueue {

    35 

    36     private static Reference r = null;

    37 

    38     private static Thread findThread(String name) {

    39         /* Find reference-handler thread */

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

    41         for (ThreadGroup tgn = tg;

    42              tgn != null;

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

    44         int nt = tg.activeCount();

    45         Thread[] ts = new Thread[nt];

    46         tg.enumerate(ts);

    47         Thread refHandler = null;

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

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

    50         }

    51         return null;

    52     }

    53 

    54     private static void fork(Runnable proc) throws InterruptedException {

    55         Thread t = new Thread(proc);

    56         t.start();

    57         t.join();

    58     }

    59 

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

    61 

    62         Thread refHandler = findThread("Reference Handler");

    63         if (refHandler == null)

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

    65         if (!refHandler.isAlive())

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

    67 

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

    69         fork(new Runnable() {

    70             public void run() {

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

    72             }});

    73 

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

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

    76             Thread.sleep(10);

    77             System.gc();

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

    79             if (i >= 10)

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

    81         }

    82 

    83         /* Check that the handler is still alive */

    84         if (!refHandler.isAlive())

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

    86 

    87     }

    88 

    89 }