public void registerListener(DuperModelListener listener) {
        applicationsById.values().forEach(listener::applicationActivated);
        if (isComplete) {
            listener.bootstrapComplete();
        }
        listeners.add(listener);
    }
A non-thread-safe mutable container of ApplicationInfo, also taking care of listeners on changes.

@author hakonhall
service-monitor/src/main/java/com/yahoo/vespa/service/duper/DuperModel.java