@Override
    final void request(long n) {
        final SubscriptionImpl subscription = this.subscription;
        // A user cannot access subscription without subscribing.
        assert subscription != null;

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