presto-main/src/main/java/io/prestosql/operator/SpatialIndexBuilderOperator.java/SpatialIndexBuilderOperator/isBlocked
class SpatialIndexBuilderOperator:    @Override
    public ListenableFuture<?> isBlocked()
    {
        if (indexNotNeeded != null && !indexNotNeeded.isDone()) {
            return indexNotNeeded;
        }
        return NOT_BLOCKED;
    }