The following is going into AOP, so we'll need to verify all's OK on our end (at times we hack into AOP internals):

[kabir@~/sourcecontrol/jboss-aop/branches/Branch_2_1/subversion/aop]
$svn diff -r87077:87081 src/main/java/org/jboss/aop/Advisor.java
Index: src/main/java/org/jboss/aop/Advisor.java
===================================================================
--- src/main/java/org/jboss/aop/Advisor.java (revision 87077)
+++ src/main/java/org/jboss/aop/Advisor.java (revision 87081)
@@ -82,6 +82,7 @@
 import org.jboss.metadata.spi.signature.MethodSignature;
 import org.jboss.util.NestedRuntimeException;
 import org.jboss.util.NotImplementedException;
+import org.jboss.util.collection.ConcurrentSet;

 /**
 * Manages the interceptor chains of an aspect context (usually, this context is
@@ -176,7 +177,7 @@
 /** Contains all the interceptor instances applied to this context. */
 protected HashMap<AspectDefinition, Map<String, Interceptor>> adviceInterceptors = new HashMap<AspectDefinition, Map<String, Interceptor>>();
 /** Contains all definitions of PER_INSTANCE aspects applied to this context. */
- protected volatile CopyOnWriteArraySet<AspectDefinition> perInstanceAspectDefinitions = UnmodifiableEmptyCollections.EMPTY_COPYONWRITE_ARRAYSET;
+ protected volatile Set<AspectDefinition> perInstanceAspectDefinitions = UnmodifiableEmptyCollections.EMPTY_CONCURRENT_SET;
 /** Contains all definitions of PER_JOINPOINT scoped aspects applied to this sccontext*/
 protected volatile ConcurrentHashMap<AspectDefinition, Set<Joinpoint>> perInstanceJoinpointAspectDefinitions = UnmodifiableEmptyCollections.EMPTY_CONCURRENT_HASHMAP;
 /** The {@code java.lang.String} class */
@@ -2079,13 +2080,13 @@

 protected void initPerInstanceAspectDefinitionsSet()
 {
- if (perInstanceAspectDefinitions == UnmodifiableEmptyCollections.EMPTY_COPYONWRITE_ARRAYSET)
+ if (perInstanceAspectDefinitions == UnmodifiableEmptyCollections.EMPTY_CONCURRENT_SET)
 {
 synchronized(lazyCollectionLock)
 {
- if (perInstanceAspectDefinitions == UnmodifiableEmptyCollections.EMPTY_COPYONWRITE_ARRAYSET)
+ if (perInstanceAspectDefinitions == UnmodifiableEmptyCollections.EMPTY_CONCURRENT_SET)
 {
- perInstanceAspectDefinitions = new CopyOnWriteArraySet<AspectDefinition>();
+ perInstanceAspectDefinitions = new ConcurrentSet<AspectDefinition>();
 }
 }
 }