Test with the Auction sample with the java test client. Typical test involves 30 clients joining the auction push group. During the test startup phase I generally get one or two of the following Exceptions:

java.util.ConcurrentModificationException
    at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
    at java.util.AbstractList$Itr.next(AbstractList.java:343)
    at org.icepush.LocalNotificationBroadcaster.broadcast(LocalNotificationBroadcaster.java:100)
    at org.icepush.LocalPushGroupManager$Notification.run(LocalPushGroupManager.java:364)
    at org.icepush.LocalPushGroupManager$QueueConsumerTask.run(LocalPushGroupManager.java:448)
    at java.util.TimerThread.mainLoop(Timer.java:512)
    at java.util.TimerThread.run(Timer.java:462)
12-Sep-2012 2:39:34 PM org.icepush.servlet.AsyncAdaptingServlet <init>

The application runs fine after the startup phase. It's unclear whether the client actually was able to join the group or not.



Looking at the code, the broadcast method iterates over the set of receivers

 for (Receiver receiver : receivers) {
            receiverConfirmedMapLock.lock();
            try {
                if (receiverConfirmedMap.get(receiver) == ConfirmationStatus.FALSE) {
                    receiver.receive(notifiedPushIds, receiverConfirmationMap.remove(receiver));
                }
            } finally {
                receiverConfirmedMapLock.unlock();
            }
        }

while the addReceiver method can freely add new receivers to the underlying collection:

    public void addReceiver(Receiver receiver) {
        receivers.add(receiver);
    }