presto-main/src/main/java/io/prestosql/spiller/FileSingleStreamSpiller.java/FileSingleStreamSpiller/spill
class FileSingleStreamSpiller:    @Override
    public ListenableFuture<?> spill(Iterator<Page> pageIterator)
    {
        requireNonNull(pageIterator, "pageIterator is null");
        checkNoSpillInProgress();
        spillInProgress = executor.submit(() -> writePages(pageIterator));
        return spillInProgress;
    }