@Override
    public synchronized void stop() {
        if (isActive.compareAndSet(true, false)) {
            if (scheduledFuture != null) {
                scheduledFuture.cancel(true);
            }
        } else {
            logger.info("Not active, no-op");
        }
    }
A default strategy for the dynamic server list updater to update.
(refactored and moved here from {@link com.netflix.loadbalancer.DynamicServerListLoadBalancer})

@author David Liu
ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/PollingServerListUpdater.java