ridljar/com/sun/star/lib/uno/helper/WeakAdapter.java

   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 package com.sun.star.lib.uno.helper;
  20 import java.lang.ref.WeakReference;
  21 import com.sun.star.uno.XAdapter;
  22 import com.sun.star.uno.XReference;
  23 import java.util.List;
  24 import java.util.Collections;
  25 import java.util.LinkedList;
  26
  27 /** An XAdapter implementation that holds a weak reference (java.lang.ref.WeakReference)
  28  *  to an object. Clients can register listener (com.sun.star.lang.XReference) which
  29  *  are notified when the object (the one which is kept weak) is being finalized. That
  30  *  is, that object is being destroyed because there are not any hard references
  31  *  to it.
  32  */
  33 public class WeakAdapter implements XAdapter
  34 {
  35     // references the XWeak implementation
  36     private final WeakReference<Object> m_weakRef;
  37     // contains XReference objects registered by addReference
  38     private final List<XReference> m_xreferenceList;
  39
  40     /**
  41      *@param component the object that is to be held weak
  42      */
  43     public WeakAdapter(Object component)
  44     {
  45         m_weakRef= new WeakReference<Object>(component);
  46         m_xreferenceList= Collections.synchronizedList( new LinkedList<XReference>());
  47     }
  48
  49     /** Called by the XWeak implementation (WeakBase) when it is being finalized.
  50      *  It is only being called once.
  51      *  The registered XReference listeners are notified. On notification they are
  52      *  to unregister themselves. The notification is thread-safe. However, it is possible
  53      *  to add a listener during the notification process, which will never receive a
  54      *  notification. To prevent this, one would have to synchronize this method with
  55      *  the addReference method. But this can result in deadlocks in a multi-threaded
  56      *  environment.
  57      */
  58     void referentDying()
  59     {
  60         //synchronized call
  61         XReference[] references= m_xreferenceList.toArray(new XReference[m_xreferenceList.size()]);
  62         for (int i= references.length; i > 0; i--)
  63         {
  64             references[i-1].dispose();
  65         }
  66     }
  67
  68     /** Method  of com.sun.star.uno.XAdapter. It is called to obtain a hard reference
  69      *  to the object which is kept weak by this instance.
  70      *  @return hard reference to the object
  71      */
  72     public Object queryAdapted()
  73     {
  74         return m_weakRef.get();
  75     }
  76
  77     /** Method of com.sun.star.uno.XAdapter. Called by clients to register listener which
  78      * are notified when the weak object is dying.
  79      *@param xReference a listener
  80      */
  81     public void removeReference(XReference xReference)
  82     {
  83         m_xreferenceList.remove(xReference);
  84     }
  85
  86     /** Method of com.sun.star.uno.XAdapter. Called by clients to unregister listeners.
  87      *@param xReference listener
  88      */
  89     public void addReference(XReference xReference)
  90     {
  91         m_xreferenceList.add(xReference);
  92     }
  93 }
  94