public synchronized void freeze() {
        super.freeze();
        executionList.execute();
    }
Freezes this class to prevent further changes. Override this to freeze internal data
structures and dependent objects. Overrides must call super.
Calling freeze on an already frozen registry must have no effect.
<p>
Notifies listeners that freezing has happened.
component/src/main/java/com/yahoo/component/provider/ListenableFreezableClass.java