presto-spi/src/main/java/io/prestosql/spi/block/LazyBlock.java/LazyBlock/addListeners
class LazyBlock:        private void addListeners(List<Consumer<Block>> listeners)
        {
            if (isLoaded()) {
                throw new IllegalStateException("Block is already loaded");
            }
            if (this.listeners == null) {
                this.listeners = new ArrayList<>();
            }
            this.listeners.addAll(listeners);
        }