private String cachingGetTargetSpec(Integer distributor, RoutingContext context, GenerationCache cache) {
            String cachedTarget = cache.get(distributor);
            if (cachedTarget != null) {
                return cachedTarget;
            }
            // Mirror _may_ be at a higher version if we race with generation read, but that is OK since
            // we'll either way get the most up-to-date mapping and the cache will be invalidated on the
            // next invocation.
            String resolvedTarget = super.getTargetSpec(distributor, context);
            cache.put(distributor, resolvedTarget);
            return resolvedTarget;
        }
Distributor index to resolved RPC spec cache for a single given Slobrok
update generation. Uses a thread safe COW map which will grow until stable.
documentapi/src/main/java/com/yahoo/documentapi/messagebus/protocol/ContentPolicy.java