private LongGauge getSubscriptionCounter(InterestKey interestKey) { LongGauge counter = subscribedClientsByInterest.get(interestKey); if (counter == null) { synchronized (subscribedClientsByInterest) { counter = subscribedClientsByInterest.get(interestKey); if (counter == null) { counter = new LongGauge(monitorConfig("subscriptions." + interestKey.getCounterName())); subscribedClientsByInterest.put(interestKey, counter); register(counter); } } } return counter; }