void requestRemovalAheadOf(int offset) {
            for (;;) {
                final int oldLastRemovalRequestedOffset = lastRemovalRequestedOffset;
                if (oldLastRemovalRequestedOffset >= offset) {
                    return;
                }
                if (lastRemovalRequestedOffsetUpdater.compareAndSet(
                        this, oldLastRemovalRequestedOffset, offset)) {
                    return;
                }
            }
        }
Invoked by the executor in {@link DownstreamSubscription}.
core/src/main/java/com/linecorp/armeria/common/stream/DefaultStreamMessageDuplicator.java