private static <T> T require(String name, Inspector object, Function<Inspector, T> mapper) {
            return requireNonNull(get(name, object, mapper));
        }
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