public long get() {
        try {
            AtomicValue<Long> value = counter.get();
            if (!value.succeeded()) {
                throw new RuntimeException("Get did not succeed");
            }
            return value.postValue();
        } catch (Exception e) {
            throw new RuntimeException("Unable to get value", e);
        }
    }
Atomically add and return resulting value.

@param delta value to add, may be negative
@return the resulting value
@throws IllegalStateException if addition fails
zkfacade/src/main/java/com/yahoo/vespa/curator/recipes/CuratorCounter.java