cli_ure/source/ure/uno/util/WeakAdapter.cs

   1 /*
   2  * This file is part of the LibreOffice project.
   3  *
   4  * This Source Code Form is subject to the terms of the Mozilla Public
   5  * License, v. 2.0. If a copy of the MPL was not distributed with this
   6  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
   7  *
   8  * This file incorporates work covered by the following license notice:
   9  *
  10  *   Licensed to the Apache Software Foundation (ASF) under one or more
  11  *   contributor license agreements. See the NOTICE file distributed
  12  *   with this work for additional information regarding copyright
  13  *   ownership. The ASF licenses this file to you under the Apache
  14  *   License, Version 2.0 (the "License"); you may not use this file
  15  *   except in compliance with the License. You may obtain a copy of
  16  *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
  17  */
  18
  19 using System;
  20 using unoidl.com.sun.star.uno;
  21 using unoidl.com.sun.star.lang;
  22
  23 namespace uno.util
  24 {
  25
  26 /** An XAdapter implementation that holds a weak reference
  27     (System.WeakReference) to an object.
  28     Clients can register listeners (unoidl.com.sun.star.lang.XReference)
  29     which are notified when the object (the one which is kept weak) is
  30     being finalized.  That is, that object is being destroyed because there
  31     are not any hard references to it.
  32 */
  33 public class WeakAdapter : XAdapter
  34 {
  35     // references the XWeak implementation
  36     private WeakReference m_weakRef;
  37     // contains XReference objects registered by addReference
  38     private delegate void XReference_dispose();
  39     private XReference_dispose m_XReference_dispose;
  40
  41     /** ctor.
  42
  43         @param obj the object that is to be held weakly
  44     */
  45     public WeakAdapter( Object obj )
  46     {
  47         m_weakRef = new WeakReference( obj );
  48         m_XReference_dispose = null;
  49     }
  50
  51     /** Called by the XWeak implementation (WeakBase) when it is being
  52         finalized.  It is only being called once.
  53         The registererd XReference listeners are notified. On notification
  54         they are  to unregister themselves. The notification is thread-safe.
  55         However, it is possible to add a listener during the notification
  56         process, which will never receive a notification.
  57         To prevent this, one would have to synchronize this method with
  58         the addReference method. But this can result in deadlocks in a
  59         multithreaded environment.
  60     */
  61     internal /* non-virtual */ void referentDying()
  62     {
  63         XReference_dispose call;
  64         lock (this)
  65         {
  66             call = m_XReference_dispose;
  67             m_XReference_dispose = null;
  68         }
  69         if (null != call)
  70             call();
  71     }
  72
  73     // XAdapter impl
  74
  75     /** Called to obtain a hard reference o the object which is kept weakly
  76         by this instance.
  77
  78         @return hard reference to the object
  79     */
  80     public Object queryAdapted()
  81     {
  82         return m_weakRef.Target;
  83     }
  84     /** Called by clients to register listener which are notified when the
  85         weak object is dying.
  86
  87         @param xReference a listener
  88     */
  89     public void removeReference( XReference xReference )
  90     {
  91         lock (this)
  92         {
  93             m_XReference_dispose -=
  94                 new XReference_dispose( xReference.dispose );
  95         }
  96     }
  97     /** Called by clients to unregister listeners.
  98
  99         @param xReference a listener
 100     */
 101     public void addReference( XReference xReference )
 102     {
 103         lock (this)
 104         {
 105             m_XReference_dispose +=
 106                 new XReference_dispose( xReference.dispose );
 107         }
 108     }
 109 }
 110
 111 }