private JRTClientConfigRequest pollQueue(long timeoutMillis) {
        try {
            // Only valid responses are on queue, no need to validate
            JRTClientConfigRequest request = responseQueue.poll(timeoutMillis, TimeUnit.MILLISECONDS);
            return (request instanceof EOFJRTClientConfigRequest) ? null : request;
        } catch (InterruptedException e1) {
            throw new ConfigInterruptedException(e1);
        }
    }
Polls the callback queue for new config

@param timeoutMillis timeout when polling (returns after at most this time)
config/src/main/java/com/yahoo/config/subscription/impl/JRTConfigSubscription.java