@Override
        public void onSubscribe(Subscription subscription) {
            this.subscription = subscription;
            subscription.request(Long.MAX_VALUE);
        }
Connect the underlying completion subscriber to this barrier in order
to track cancel signals and pass them on to the write barrier.
spring/boot3-webflux-autoconfigure/src/main/java/com/linecorp/armeria/spring/web/reactive/ChannelSendOperator.java