@Override
        public void request(long n) {
            final Subscription s = subscription;
            if (s == null) {
                return;
            }
            if (state == State.READY_TO_WRITE) {
                s.request(n);
                return;
            }
            synchronized (this) {
                if (writeSubscriber != null) {
                    if (state == State.EMITTING_CACHED_SIGNALS) {
                        demandBeforeReadyToWrite = n;
                        return;
                    }
                    try {
                        state = State.EMITTING_CACHED_SIGNALS;
                        if (emitCachedSignals()) {
                            return;
                        }
                        n = n + demandBeforeReadyToWrite - 1;
                        if (n == 0) {
                            return;
                        }
                    } finally {
                        state = State.READY_TO_WRITE;
                    }
                }
            }
            s.request(n);
        }
The actual writeSubscriber from the HTTP server adapter.
spring/boot3-webflux-autoconfigure/src/main/java/com/linecorp/armeria/spring/web/reactive/ChannelSendOperator.java