Index: lucene/src/java/org/apache/lucene/index/IndexReader.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/IndexReader.java	(revision 1221367)
+++ lucene/src/java/org/apache/lucene/index/IndexReader.java	(working copy)
@@ -22,10 +22,11 @@
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.util.Collection;
+import java.util.Collections;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
-import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import org.apache.lucene.document.Document;
@@ -36,7 +37,6 @@
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.CommandLineUtil;
-import org.apache.lucene.util.MapBackedSet;
 import org.apache.lucene.util.ReaderUtil;         // for javadocs
 
 /** IndexReader is an abstract class, providing an interface for accessing an
@@ -84,7 +84,7 @@
   }
 
   private final Set<ReaderClosedListener> readerClosedListeners = 
-      new MapBackedSet<ReaderClosedListener>(new ConcurrentHashMap<ReaderClosedListener, Boolean>());
+      Collections.synchronizedSet(new LinkedHashSet<ReaderClosedListener>());
 
   /** Expert: adds a {@link ReaderClosedListener}.  The
    * provided listener will be invoked when this reader is closed.
@@ -104,8 +104,10 @@
   }
 
   private final void notifyReaderClosedListeners() {
-    for(ReaderClosedListener listener : readerClosedListeners) {
-      listener.onClose(this);
+    synchronized(readerClosedListeners) {
+      for(ReaderClosedListener listener : readerClosedListeners) {
+        listener.onClose(this);
+      }
     }
   }
 
Index: lucene/src/java/org/apache/lucene/index/SegmentCoreReaders.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/SegmentCoreReaders.java	(revision 1221367)
+++ lucene/src/java/org/apache/lucene/index/SegmentCoreReaders.java	(working copy)
@@ -18,8 +18,9 @@
  */
 
 import java.io.IOException;
+import java.util.Collections;
+import java.util.LinkedHashSet;
 import java.util.Set;
-import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import org.apache.lucene.codecs.Codec;
@@ -34,7 +35,6 @@
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.store.IOContext;
 import org.apache.lucene.util.IOUtils;
-import org.apache.lucene.util.MapBackedSet;
 
 /** Holds core readers that are shared (unchanged) when
  * SegmentReader is cloned or reopened */
@@ -67,8 +67,8 @@
   CompoundFileDirectory cfsReader;
   CompoundFileDirectory storeCFSReader;
 
-  final Set<CoreClosedListener> coreClosedListeners = 
-      new MapBackedSet<CoreClosedListener>(new ConcurrentHashMap<CoreClosedListener, Boolean>());
+  private final Set<CoreClosedListener> coreClosedListeners = 
+      Collections.synchronizedSet(new LinkedHashSet<CoreClosedListener>());
   
   SegmentCoreReaders(SegmentReader owner, Directory dir, SegmentInfo si, IOContext context, int termsIndexDivisor) throws IOException {
     
@@ -138,12 +138,26 @@
     if (ref.decrementAndGet() == 0) {
       IOUtils.close(fields, perDocProducer, termVectorsReaderOrig,
           fieldsReaderOrig, cfsReader, storeCFSReader, norms);
+      notifyCoreClosedListeners();
+    }
+  }
+  
+  private final void notifyCoreClosedListeners() {
+    synchronized(coreClosedListeners) {
       for (CoreClosedListener listener : coreClosedListeners) {
         listener.onClose(owner);
       }
     }
   }
+
+  void addCoreClosedListener(CoreClosedListener listener) {
+    coreClosedListeners.add(listener);
+  }
   
+  void removeCoreClosedListener(CoreClosedListener listener) {
+    coreClosedListeners.remove(listener);
+  }
+
   synchronized void openDocStores(SegmentInfo si) throws IOException {
     
     assert si.name.equals(segment);
Index: lucene/src/java/org/apache/lucene/index/SegmentReader.java
===================================================================
--- lucene/src/java/org/apache/lucene/index/SegmentReader.java	(revision 1221367)
+++ lucene/src/java/org/apache/lucene/index/SegmentReader.java	(working copy)
@@ -595,12 +595,12 @@
   /** Expert: adds a CoreClosedListener to this reader's shared core */
   public void addCoreClosedListener(CoreClosedListener listener) {
     ensureOpen();
-    core.coreClosedListeners.add(listener);
+    core.addCoreClosedListener(listener);
   }
   
   /** Expert: removes a CoreClosedListener from this reader's shared core */
   public void removeCoreClosedListener(CoreClosedListener listener) {
     ensureOpen();
-    core.coreClosedListeners.remove(listener);
+    core.removeCoreClosedListener(listener);
   }
 }