docs: public void close()
     {
        if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) SibTr.entry(this, tc, "close");
        synchronized(this)
        {
           if (closed)
           {
              idToProxyQueueMap.clear();
              factory.groupCloseNotification(conversation, this);
           } 
        }      
        if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) SibTr.exit(this, tc, "close");
     }