presto-main/src/main/java/io/prestosql/operator/exchange/PageReference.java/PageReference/PageReference
class PageReference:    public PageReference(Page page, int referenceCount, Runnable onFree)
    {
        this.page = requireNonNull(page, "page is null");
        this.onFree = requireNonNull(onFree, "onFree is null");
        checkArgument(referenceCount >= 1, "referenceCount must be at least 1");
        this.referenceCount = new AtomicInteger(referenceCount);
    }