1 /*

     2  * Copyright 1999-2008 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.  Sun designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Sun in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

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

    23  * have any questions.

    24  */

    25 

    26 package com.sun.jmx.mbeanserver;

    27 

    28 import java.lang.ref.WeakReference;

    29 import java.util.concurrent.ThreadPoolExecutor;

    30 

    31 /**

    32  * <p>A factory for ThreadPoolExecutor objects that allows the same object to

    33  * be shared by all users of the factory that are in the same ThreadGroup.</p>

    34  */

    35 // We return a ThreadPoolExecutor rather than the more general ExecutorService

    36 // because we need to be able to call allowCoreThreadTimeout so that threads in

    37 // the pool will eventually be destroyed when the pool is no longer in use.

    38 // Otherwise these threads would keep the ThreadGroup alive forever.

    39 public class PerThreadGroupPool<T extends ThreadPoolExecutor> {

    40     private final WeakIdentityHashMap<ThreadGroup, WeakReference<T>> map =

    41             WeakIdentityHashMap.make();

    42 

    43     public static interface Create<T extends ThreadPoolExecutor> {

    44         public T createThreadPool(ThreadGroup group);

    45     }

    46 

    47     private PerThreadGroupPool() {}

    48 

    49     public static <T extends ThreadPoolExecutor> PerThreadGroupPool<T> make() {

    50         return new PerThreadGroupPool<T>();

    51     }

    52 

    53     public synchronized T getThreadPoolExecutor(Create<T> create) {

    54         // Find out if there's already an existing executor for the calling

    55         // thread and reuse it. Otherwise, create a new one and store it in

    56         // the executors map. If there is a SecurityManager, the group of

    57         // System.getSecurityManager() is used, else the group of the calling

    58         // thread.

    59         SecurityManager s = System.getSecurityManager();

    60         ThreadGroup group = (s != null) ? s.getThreadGroup() :

    61             Thread.currentThread().getThreadGroup();

    62         WeakReference<T> wr = map.get(group);

    63         T executor = (wr == null) ? null : wr.get();

    64         if (executor == null) {

    65             executor = create.createThreadPool(group);

    66             executor.allowCoreThreadTimeOut(true);

    67             map.put(group, new WeakReference<T>(executor));

    68         }

    69         return executor;

    70     }

    71 }