@Override
            public void onSubscribe(Subscription subscription) {
                // Cancel the subscription when the demand is 0.
                this.subscription = subscription;
                subscription.request(1);
            }
A test for the {@link SignalQueue} in {@link DefaultStreamMessageDuplicator}.
Queue expansion behaves differently when odd/even number head wrap-around happens.
core/src/test/java/com/linecorp/armeria/common/stream/StreamMessageDuplicatorTest.java