@Override
        public void onError(Throwable ex) {
            try {
                completionSubscriber.onError(ex);
            } finally {
                writeBarrier.releaseCachedItem();
            }
        }
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