code: public TopicRecord retrieveCallbackFromConnectionIndex(
      ConnectionImpl connection,
      ConsumerSetChangeCallback callback)
    {
      if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
          SibTr.entry(
            tc,
            "retrieveCallbackFromConnectionIndex",
            new Object[] {connection, callback });
  
      TopicRecord tRecord = null;
  
      if(_callbackIndex.containsKey(connection))
      {
        // Have found registered callbacks for this connection
        Map connMap = (HashMap)_callbackIndex.get(connection);
  
        // Locate the specific callback
        tRecord = (TopicRecord)connMap.get(callback);
      }
  
      if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled())
        SibTr.exit(tc, "retrieveCallbackFromConnectionIndex", tRecord);
  
      return tRecord;
    }
docs: Method retrieveCallbackFromConnectionIndex
  
  Retrieves an existing callback from the callback index.
  
  @param topicExpression
  @param isWildcarded
  @param callback
  @return