Index: src/main/java/org/apache/jackrabbit/core/state/ItemStateReferenceCache.java
===================================================================
--- src/main/java/org/apache/jackrabbit/core/state/ItemStateReferenceCache.java	(revision 605226)
+++ src/main/java/org/apache/jackrabbit/core/state/ItemStateReferenceCache.java	(working copy)
@@ -42,6 +42,7 @@
  * collector if they are thus rendered weakly reachable.
  * </li>
  * </ul>
+ * This implementation of ItemStateCache is thread-safe.
  */
 public class ItemStateReferenceCache implements ItemStateCache, Dumpable {
 
@@ -86,7 +87,7 @@
     /**
      * {@inheritDoc}
      */
-    public boolean isCached(ItemId id) {
+    public synchronized boolean isCached(ItemId id) {
         // check primary cache
         return refs.contains(id);
     }
@@ -94,7 +95,7 @@
     /**
      * {@inheritDoc}
      */
-    public ItemState retrieve(ItemId id) {
+    public synchronized ItemState retrieve(ItemId id) {
         // fake call to update stats of secondary cache
         cache.retrieve(id);
 
@@ -105,7 +106,7 @@
     /**
      * {@inheritDoc}
      */
-    public void cache(ItemState state) {
+    public synchronized void cache(ItemState state) {
         ItemId id = state.getId();
         if (refs.contains(id)) {
             log.warn("overwriting cached entry " + id);
@@ -120,7 +121,7 @@
     /**
      * {@inheritDoc}
      */
-    public void evict(ItemId id) {
+    public synchronized void evict(ItemId id) {
         // fake call to update stats of secondary cache
         cache.evict(id);
         // remove from primary cache
@@ -130,14 +131,14 @@
     /**
      * {@inheritDoc}
      */
-    public void dispose() {
+    public synchronized void dispose() {
         cache.dispose();
     }
 
     /**
      * {@inheritDoc}
      */
-    public void evictAll() {
+    public synchronized void evictAll() {
         // fake call to update stats of secondary cache
         cache.evictAll();
         // remove all weak references from primary cache
@@ -147,7 +148,7 @@
     /**
      * {@inheritDoc}
      */
-    public void update(ItemId id) {
+    public synchronized void update(ItemId id) {
         // delegate
         cache.update(id);
     }
@@ -155,7 +156,7 @@
     /**
      * {@inheritDoc}
      */
-    public boolean isEmpty() {
+    public synchronized boolean isEmpty() {
         // check primary cache
         return refs.isEmpty();
     }
@@ -163,23 +164,49 @@
     /**
      * {@inheritDoc}
      */
-    public int size() {
+    public synchronized int size() {
         // size of primary cache
         return refs.size();
     }
 
     /**
      * {@inheritDoc}
+     * <p/>
+     * The returned Set is not synchronized. The caller must ensure that
+     * it manually synchronizes access to the Set. Example:
+     * <pre>
+     * ItemStateCache cache = new ItemStateReferenceCache(...);
+     * synchronized (cache) {
+     *     Set keys = cache.keySet();
+     *     for (Iterator it = keys.iterator(); it.hasNext(); ) {
+     *         Object item = it.next();
+     *         // do something with item
+     *     }
+     * }
+     * </pre>
      */
-    public Set keySet() {
+    public synchronized Set keySet() {
         // keys of primary cache
         return Collections.unmodifiableSet(refs.keySet());
     }
 
     /**
      * {@inheritDoc}
+     * <p/>
+     * The returned collection is not synchronized. The caller must ensure that
+     * it manually synchronizes access to the collection. Example:
+     * <pre>
+     * ItemStateCache cache = new ItemStateReferenceCache(...);
+     * synchronized (cache) {
+     *     Collection values = cache.values();
+     *     for (Iterator it = values.iterator(); it.hasNext(); ) {
+     *         Object item = it.next();
+     *         // do something with item
+     *     }
+     * }
+     * </pre>
      */
-    public Collection values() {
+    public synchronized Collection values() {
         // values of primary cache
         return Collections.unmodifiableCollection(refs.values());
     }
@@ -188,7 +215,7 @@
     /**
      * {@inheritDoc}
      */
-    public void dump(PrintStream ps) {
+    public synchronized void dump(PrintStream ps) {
         ps.println("ItemStateReferenceCache (" + this + ")");
         ps.println();
         ps.print("[refs] ");
Index: src/main/java/org/apache/jackrabbit/core/state/LocalItemStateManager.java
===================================================================
--- src/main/java/org/apache/jackrabbit/core/state/LocalItemStateManager.java	(revision 605226)
+++ src/main/java/org/apache/jackrabbit/core/state/LocalItemStateManager.java	(working copy)
@@ -35,7 +35,7 @@
      * cache of weak references to ItemState objects issued by this
      * ItemStateManager
      */
-    private final ItemStateReferenceCache cache;
+    private final ItemStateCache cache;
 
     /**
      * Shared item state manager
@@ -140,7 +140,7 @@
         }
 
         // check cache. synchronized to ensure an entry is not created twice.
-        synchronized (cache) {
+        synchronized (this) {
             state = cache.retrieve(id);
             if (state == null) {
                 // regular behaviour
@@ -336,8 +336,11 @@
 
         // JCR-798: copy cached item states to array
         // to avoid ConcurrentModificationException
-        ItemState[] isa = (ItemState[]) cache.values().toArray(
-                new ItemState[cache.size()]);
+        ItemState[] isa;
+        synchronized (cache) {
+            isa = (ItemState[]) cache.values().toArray(
+                            new ItemState[cache.size()]);
+        }
         for (int i = 0; i < isa.length; i++) {
             ItemState state = isa[i];
             if (state != null) {