001    // Copyright 2006, 2007, 2010 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    // http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry5.ioc.internal.services;
016    
017    import java.lang.ref.WeakReference;
018    import java.util.Iterator;
019    import java.util.List;
020    
021    import org.apache.tapestry5.ioc.annotations.PreventServiceDecoration;
022    import org.apache.tapestry5.ioc.internal.util.CollectionFactory;
023    import org.apache.tapestry5.services.UpdateListener;
024    import org.apache.tapestry5.services.UpdateListenerHub;
025    
026    @PreventServiceDecoration
027    public class UpdateListenerHubImpl implements UpdateListenerHub
028    {
029        private final List<WeakReference<UpdateListener>> listeners = CollectionFactory.newThreadSafeList();
030    
031        public void addUpdateListener(UpdateListener listener)
032        {
033            assert listener != null;
034            listeners.add(new WeakReference<UpdateListener>(listener));
035        }
036    
037        /**
038         * Notifies all {@link UpdateListener}s.
039         */
040        public void fireCheckForUpdates()
041        {
042            List<WeakReference<UpdateListener>> deadReferences = CollectionFactory.newList();
043    
044            Iterator<WeakReference<UpdateListener>> i = listeners.iterator();
045    
046            while (i.hasNext())
047            {
048                WeakReference<UpdateListener> reference = i.next();
049    
050                UpdateListener listener = reference.get();
051    
052                if (listener == null)
053                    deadReferences.add(reference);
054                else
055                    listener.checkForUpdates();
056            }
057    
058            if (!deadReferences.isEmpty())
059                listeners.removeAll(deadReferences);
060        }
061    }