Index: src/java/org/apache/lucene/search/CachingSpanFilter.java
===================================================================
--- src/java/org/apache/lucene/search/CachingSpanFilter.java	(revision 832941)
+++ src/java/org/apache/lucene/search/CachingSpanFilter.java	(working copy)
@@ -28,13 +28,15 @@
  * filters to simply filter, and then wrap with this class to add caching.
  */
 public class CachingSpanFilter extends SpanFilter {
-  protected SpanFilter filter;
+  private SpanFilter filter;
 
   /**
-   * A transient Filter cache.
+   * A transient Filter cache (package private because of test)
    */
-  protected transient Map<IndexReader,SpanFilterResult> cache;
+  private transient Map<IndexReader,SpanFilterResult> cache;
 
+  private final Object lock = new Object();
+
   /**
    * @param filter Filter to cache results of
    */
@@ -49,19 +51,20 @@
   }
   
   private SpanFilterResult getCachedResult(IndexReader reader) throws IOException {
-    SpanFilterResult result = null;
-    if (cache == null) {
-      cache = new WeakHashMap<IndexReader,SpanFilterResult>();
-    }
+    synchronized(lock) {
+      SpanFilterResult result = null;
+      if (cache == null) {
+        cache = new WeakHashMap<IndexReader,SpanFilterResult>();
+      }
 
-    synchronized (cache) {  // check cache
       result = cache.get(reader);
       if (result == null) {
         result = filter.bitSpans(reader);
         cache.put(reader, result);
       }
+      
+      return result;
     }
-    return result;
   }
 
 
Index: src/java/org/apache/lucene/search/CachingWrapperFilter.java
===================================================================
--- src/java/org/apache/lucene/search/CachingWrapperFilter.java	(revision 832941)
+++ src/java/org/apache/lucene/search/CachingWrapperFilter.java	(working copy)
@@ -29,12 +29,14 @@
  * filters to simply filter, and then wrap with this class to add caching.
  */
 public class CachingWrapperFilter extends Filter {
-  protected Filter filter;
+  Filter filter;
 
   /**
-   * A transient Filter cache.
+   * A transient Filter cache (package private because of test)
    */
-  protected transient Map<IndexReader, DocIdSet> cache;
+  transient Map<IndexReader, DocIdSet> cache;
+  
+  private final Object lock = new Object();
 
   /**
    * @param filter Filter to cache results of
@@ -63,28 +65,24 @@
   
   @Override
   public DocIdSet getDocIdSet(IndexReader reader) throws IOException {
-    if (cache == null) {
-      cache = new WeakHashMap<IndexReader, DocIdSet>();
-    }
+    synchronized(lock) {
+      if (cache == null) {
+        cache = new WeakHashMap<IndexReader,DocIdSet>();
+      }
 
-    DocIdSet cached = null;
-    synchronized (cache) {  // check cache
-      cached = cache.get(reader);
-    }
+      final DocIdSet cached = cache.get(reader);
+      if (cached != null) {
+        return cached;
+      }
 
-    if (cached != null) {
-      return cached;
-    }
+      final DocIdSet docIdSet = docIdSetToCache(filter.getDocIdSet(reader), reader);
 
-    final DocIdSet docIdSet = docIdSetToCache(filter.getDocIdSet(reader), reader);
-
-    if (docIdSet != null) {
-      synchronized (cache) {  // update cache
+      if (docIdSet != null) {
         cache.put(reader, docIdSet);
       }
+      
+      return docIdSet;
     }
-
-    return docIdSet;
   }
 
   @Override