@Override
        public void request(long n) {
            if (n <= 0) {
                final IllegalArgumentException exception = new IllegalArgumentException(
                        "Expecting only positive requests for parts");
                abort(exception);
                return;
            }
            if (executor.inEventLoop()) {
                request0(n);
            } else {
                executor.execute(() -> request0(n));
            }
        }
For hiding Subscriber interface from MultipartDecoder.
Subscribing {@code DecodedHttpStreamMessage<BodyPart>} and delegating to external subscriber.
core/src/main/java/com/linecorp/armeria/common/multipart/MultipartDecoder.java