private void handleCloseEvent(SubscriptionImpl subscription, CloseEvent o) {
        if (setState(State.CLOSED, State.CLEANUP)) {
            notifySubscriberOfCloseEvent(subscription, o);
        }
    }
Invoked whenever a new demand is requested.
@param n Newly requested demand
core/src/main/java/com/linecorp/armeria/common/stream/DefaultStreamMessage.java