Clover coverage report - Code Coverage for hivemind release 1.0-beta-2
Coverage timestamp: Sun Aug 1 2004 14:03:45 EDT
file stats: LOC: 187   Methods: 10
NCLOC: 97   Classes: 2
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 Source file Conditionals Statements Methods TOTAL
EventListenerList.java 100% 100% 100% 100%
coverage
 1   
 //  Copyright 2004 The Apache Software Foundation
 2   
 //
 3   
 // Licensed under the Apache License, Version 2.0 (the "License");
 4   
 // you may not use this file except in compliance with the License.
 5   
 // You may obtain a copy of the License at
 6   
 //
 7   
 //     http://www.apache.org/licenses/LICENSE-2.0
 8   
 //
 9   
 // Unless required by applicable law or agreed to in writing, software
 10   
 // distributed under the License is distributed on an "AS IS" BASIS,
 11   
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 12   
 // See the License for the specific language governing permissions and
 13   
 // limitations under the License.
 14   
 
 15   
 package org.apache.hivemind.util;
 16   
 
 17   
 import java.util.Iterator;
 18   
 
 19   
 /**
 20   
  * Convienience class for tracking a list of event listeners. Works efficiently
 21   
  * (using a copy-on-write approach) to iterating through the listeners in
 22   
  * the list even when the list of listeners may be modified.
 23   
  * 
 24   
  * <p>
 25   
  * EventListenerList <em>is</em> thread-safe.
 26   
  *
 27   
  * @author Howard Lewis Ship
 28   
  */
 29   
 public class EventListenerList
 30   
 {
 31   
     private static final int START_SIZE = 5;
 32   
 
 33   
     private Object[] _listeners;
 34   
     private int _count;
 35   
     private int _iteratorCount;
 36   
     private int _uid;
 37   
 
 38   
     private class ListenerIterator implements Iterator
 39   
     {
 40   
         private Object[] _localListeners;
 41   
         private int _localCount;
 42   
         private int _localUid;
 43   
         private int _pos;
 44   
 
 45  135
         private ListenerIterator()
 46   
         {
 47  135
             _localListeners = _listeners;
 48  135
             _localCount = _count;
 49  135
             _localUid = _uid;
 50   
         }
 51   
 
 52  218
         public boolean hasNext()
 53   
         {
 54  218
             if (_pos >= _localCount)
 55   
             {
 56   
                 // If _listeners has not been recopied during the lifespan
 57   
                 // of this iterator, then knock the count down by one.
 58   
 
 59  34
                 adjustIteratorCount(_localUid);
 60   
 
 61  34
                 _localListeners = null;
 62  34
                 _localCount = 0;
 63  34
                 _localUid = -1;
 64  34
                 _pos = 0;
 65   
 
 66  34
                 return false;
 67   
             }
 68   
 
 69  184
             return true;
 70   
         }
 71   
 
 72  199
         public Object next()
 73   
         {
 74  199
             return _localListeners[_pos++];
 75   
         }
 76   
 
 77  1
         public void remove()
 78   
         {
 79  1
             throw new UnsupportedOperationException();
 80   
         }
 81   
 
 82   
     }
 83   
 
 84   
     /**
 85   
      * Returns an Iterator used to find all the listeners previously added.
 86   
      * The order in which listeners are returned is not guaranteed.
 87   
      * Currently, you may not invoke <code>remove()</code> on the Iterator.
 88   
      * 
 89   
      * <p>
 90   
      * Invoking this method takes a "snapshot" of the current list of listeners. 
 91   
      * You may invoke {@link #addListener(Object)} or {@link #removeListener(Object)},
 92   
      * but that won't affect the sequence of listeners returned by the Iterator.
 93   
      */
 94  135
     public synchronized Iterator getListeners()
 95   
     {
 96  135
         _iteratorCount++;
 97   
 
 98  135
         return new ListenerIterator();
 99   
     }
 100   
 
 101   
     /**
 102   
      * Adds a new listener to the list of listeners. The same instance
 103   
      * will may be added multiple times.
 104   
      */
 105  853
     public synchronized void addListener(Object listener)
 106   
     {
 107  853
         copyOnWrite(_count + 1);
 108   
 
 109  853
         _listeners[_count] = listener;
 110   
 
 111  853
         _count++;
 112   
     }
 113   
 
 114   
     /**
 115   
      * Removes a listener from the list.  Does nothing if the listener
 116   
      * is not already in the list. Comparison is based on identity, not equality.
 117   
      * If the listener is in the list multiple times, only a single
 118   
      * instance is removed.
 119   
      */
 120  108
     public synchronized void removeListener(Object listener)
 121   
     {
 122  108
         for (int i = 0; i < _count; i++)
 123   
         {
 124  143
             if (_listeners[i] == listener)
 125   
             {
 126  107
                 removeListener(i);
 127  107
                 return;
 128   
             }
 129   
         }
 130   
     }
 131   
 
 132  107
     private void removeListener(int index)
 133   
     {
 134  107
         copyOnWrite(_count);
 135   
 
 136   
         // Move the last listener in the list into the index to be removed.
 137   
 
 138  107
         _listeners[index] = _listeners[_count - 1];
 139   
 
 140   
         // Null out the old position.
 141   
 
 142  107
         _listeners[_count - 1] = null;
 143   
 
 144  107
         _count--;
 145   
     }
 146   
 
 147   
     /**
 148   
      * Copies the array before an update operation if necessary (because there
 149   
      * is a known iterator for the current array, or because the 
 150   
      * array is not large enough).
 151   
      */
 152  960
     private void copyOnWrite(int requiredSize)
 153   
     {
 154  960
         int size = _listeners == null ? 0 : _listeners.length;
 155   
 
 156  960
         if (_iteratorCount > 0 || size < requiredSize)
 157   
         {
 158  314
             int nominalSize = (size == 0) ? START_SIZE : 2 * size;
 159   
 
 160   
             // Don't grow the array if we don't need to...
 161  314
             if (size >= requiredSize)
 162   
             {
 163  106
                 nominalSize = size;
 164   
             }
 165   
 
 166  314
             int newSize = Math.max(requiredSize, nominalSize);
 167   
 
 168  314
             Object[] newListeners = new Object[newSize];
 169   
 
 170  314
             if (_count > 0)
 171  203
                 System.arraycopy(_listeners, 0, newListeners, 0, _count);
 172   
 
 173  314
             _listeners = newListeners;
 174   
 
 175   
             // No iterators on the *new* array
 176  314
             _iteratorCount = 0;
 177  314
             _uid++;
 178   
         }
 179   
     }
 180   
 
 181  34
     private synchronized void adjustIteratorCount(int iteratorUid)
 182   
     {
 183  34
         if (_uid == iteratorUid)
 184  27
             _iteratorCount--;
 185   
     }
 186   
 }
 187