@SuppressWarnings("unchecked")
    @Override
    public void handleRequestDone(Request req) {
        RequestContext context = (RequestContext) req.getContext();
        JRTConfigSubscription<ConfigInstance> sub = context.sub;
        try {
            doHandle(sub, context.jrtReq, context.connection);
        } catch (RuntimeException e) {
            // Sets this field, it will get thrown from the user thread
            sub.setException(e);
        }
    }
Requests the config for the {@link com.yahoo.config.ConfigInstance} on the given {@link ConfigSubscription}

@param sub a subscription
config/src/main/java/com/yahoo/config/subscription/impl/JRTConfigRequester.java