@Override
    public boolean nextConfig(long timeoutMillis) {
        JRTClientConfigRequest response = pollForNewConfig(timeoutMillis);
        if (response == null) return newConfigOrException();

        log.log(FINE, () -> "Polled queue and found config " + response);
        // Might set the following (caller must check):
        // generation, generation changed, config, config changed
        // Important: it never <em>resets</em> those flags, we must persist that state until the
        // ConfigSubscriber clears it
        if (response.hasUpdatedGeneration()) {
            setApplyOnRestart(response.responseIsApplyOnRestart());
            if (response.hasUpdatedConfig()) {
                setNewConfig(response);
            } else {
                setNewConfigAndGeneration(response);
            }
        }

        return newConfigOrException();
    }
A queue containing responses (requests that got a callback from JRT) that has not yet been handled.
config/src/main/java/com/yahoo/config/subscription/impl/JRTConfigSubscription.java