1 /*

     2  * Copyright (c) 2003, 2015, Oracle and/or its affiliates. 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.  Oracle designates this

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

     9  * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 

    26 package sun.management;

    27 

    28 import javax.management.ListenerNotFoundException;

    29 import javax.management.MBeanNotificationInfo;

    30 import javax.management.Notification;

    31 import javax.management.NotificationEmitter;

    32 import javax.management.NotificationFilter;

    33 import javax.management.NotificationListener;

    34 

    35 import java.util.List;

    36 import java.util.ArrayList;

    37 import java.util.Collections;

    38 

    39 /**

    40  * Abstract helper class for notification emitter support.

    41  */

    42 public abstract class NotificationEmitterSupport implements NotificationEmitter {

    43 

    44     protected NotificationEmitterSupport() {

    45     }

    46 

    47     private Object listenerLock = new Object();

    48 

    49     // Implementation of NotificationEmitter interface

    50     // Cloned from JMX NotificationBroadcasterSupport class.

    51     public void addNotificationListener(NotificationListener listener,

    52                                         NotificationFilter filter,

    53                                         Object handback) {

    54 

    55         if (listener == null) {

    56             throw new IllegalArgumentException ("Listener can't be null") ;

    57         }

    58 

    59         /* Adding a new listener takes O(n) time where n is the number

    60            of existing listeners.  If you have a very large number of

    61            listeners performance could degrade.  That's a fairly

    62            surprising configuration, and it is hard to avoid this

    63            behaviour while still retaining the property that the

    64            listenerList is not synchronized while notifications are

    65            being sent through it.  If this becomes a problem, a

    66            possible solution would be a multiple-readers single-writer

    67            setup, so any number of sendNotification() calls could run

    68            concurrently but they would exclude an

    69            add/removeNotificationListener.  A simpler but less

    70            efficient solution would be to clone the listener list

    71            every time a notification is sent.  */

    72         synchronized (listenerLock) {

    73             List<ListenerInfo> newList = new ArrayList<>(listenerList.size() + 1);

    74             newList.addAll(listenerList);

    75             newList.add(new ListenerInfo(listener, filter, handback));

    76             listenerList = newList;

    77         }

    78     }

    79 

    80     public void removeNotificationListener(NotificationListener listener)

    81         throws ListenerNotFoundException {

    82 

    83         synchronized (listenerLock) {

    84             List<ListenerInfo> newList = new ArrayList<>(listenerList);

    85             /* We scan the list of listeners in reverse order because

    86                in forward order we would have to repeat the loop with

    87                the same index after a remove.  */

    88             for (int i=newList.size()-1; i>=0; i--) {

    89                 ListenerInfo li = newList.get(i);

    90 

    91                 if (li.listener == listener)

    92                     newList.remove(i);

    93             }

    94             if (newList.size() == listenerList.size())

    95                 throw new ListenerNotFoundException("Listener not registered");

    96             listenerList = newList;

    97         }

    98     }

    99 

   100     public void removeNotificationListener(NotificationListener listener,

   101                                            NotificationFilter filter,

   102                                            Object handback)

   103             throws ListenerNotFoundException {

   104 

   105         boolean found = false;

   106 

   107         synchronized (listenerLock) {

   108             List<ListenerInfo> newList = new ArrayList<>(listenerList);

   109             final int size = newList.size();

   110             for (int i = 0; i < size; i++) {

   111                 ListenerInfo li =  newList.get(i);

   112 

   113                 if (li.listener == listener) {

   114                     found = true;

   115                     if (li.filter == filter

   116                         && li.handback == handback) {

   117                         newList.remove(i);

   118                         listenerList = newList;

   119                         return;

   120                     }

   121                 }

   122             }

   123         }

   124 

   125         if (found) {

   126             /* We found this listener, but not with the given filter

   127              * and handback.  A more informative exception message may

   128              * make debugging easier.  */

   129             throw new ListenerNotFoundException("Listener not registered " +

   130                                                 "with this filter and " +

   131                                                 "handback");

   132         } else {

   133             throw new ListenerNotFoundException("Listener not registered");

   134         }

   135     }

   136 

   137     public void sendNotification(Notification notification) {

   138 

   139         if (notification == null) {

   140             return;

   141         }

   142 

   143         List<ListenerInfo> currentList;

   144         synchronized (listenerLock) {

   145             currentList = listenerList;

   146         }

   147 

   148         final int size = currentList.size();

   149         for (int i = 0; i < size; i++) {

   150             ListenerInfo li =  currentList.get(i);

   151 

   152             if (li.filter == null

   153                 || li.filter.isNotificationEnabled(notification)) {

   154                 try {

   155                     li.listener.handleNotification(notification, li.handback);

   156                 } catch (Exception e) {

   157                     e.printStackTrace();

   158                     throw new AssertionError("Error in invoking listener");

   159                 }

   160             }

   161         }

   162     }

   163 

   164     public boolean hasListeners() {

   165         synchronized (listenerLock) {

   166             return !listenerList.isEmpty();

   167         }

   168     }

   169 

   170     private class ListenerInfo {

   171         public NotificationListener listener;

   172         NotificationFilter filter;

   173         Object handback;

   174 

   175         public ListenerInfo(NotificationListener listener,

   176                             NotificationFilter filter,

   177                             Object handback) {

   178             this.listener = listener;

   179             this.filter = filter;

   180             this.handback = handback;

   181         }

   182     }

   183 

   184     /**

   185      * Current list of listeners, a List of ListenerInfo.  The object

   186      * referenced by this field is never modified.  Instead, the field

   187      * is set to a new object when a listener is added or removed,

   188      * within a synchronized(this).  In this way, there is no need to

   189      * synchronize when traversing the list to send a notification to

   190      * the listeners in it.  That avoids potential deadlocks if the

   191      * listeners end up depending on other threads that are themselves

   192      * accessing this NotificationBroadcasterSupport.

   193      */

   194     private List<ListenerInfo> listenerList = Collections.emptyList();

   195 

   196     abstract public MBeanNotificationInfo[] getNotificationInfo();

   197 }