private void notifySubscriberOfCloseEvent(SubscriptionImpl subscription, CloseEvent event) {
        if (subscription.needsDirectInvocation()) {
            notifySubscriberOfCloseEvent0(subscription, event);
        } else {
            subscription.executor().execute(() -> notifySubscriberOfCloseEvent0(subscription, event));
        }
    }
Invoked whenever a new demand is requested.
@param n Newly requested demand
core/src/main/java/com/linecorp/armeria/common/stream/DefaultStreamMessage.java