@Override
    public boolean subscribe(long timeout) {
        lastOK = Instant.now();
        requester.request(this);
        JRTClientConfigRequest req = responseQueue.peek();
        while (req == null && (Instant.now().isBefore(lastOK.plus(Duration.ofMillis(timeout))))) {
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                throw new ConfigInterruptedException(e);
            }
            req = responseQueue.peek();
        }
        return (req != null) && ! (req instanceof EOFJRTClientConfigRequest);
    }
This method should ideally throw new MissingConfig/Configuration exceptions and let the caller
catch them. However, this would make the code in JRT/File/RawSource uglier.
Alternatively, it could return a SetConfigStatus object with an int and an error message.

@param jrtRequest a config request
@return an instance of a config class (subclass of ConfigInstance)
config/src/main/java/com/yahoo/config/subscription/impl/JRTConfigSubscription.java