private static <T> T get(String name, Inspector object, Function<Inspector, T> mapper) {
            return object.field(name).valid() ? mapper.apply(object.field(name)) : null;
        }
This lock must be held to manipulate reindexing state, or by whoever has a running visitor.
clustercontroller-reindexer/src/main/java/ai/vespa/reindexing/ReindexingCurator.java