presto-main/src/main/java/io/prestosql/operator/NestedLoopJoinOperator.java/NestedLoopJoinOperator/needsInput
class NestedLoopJoinOperator:    @Override
    public boolean needsInput()
    {
        if (finishing || probePage != null) {
            return false;
        }

        if (buildPages == null) {
            Optional<NestedLoopJoinPages> nestedLoopJoinPages = tryGetFutureValue(nestedLoopJoinPagesFuture);
            if (nestedLoopJoinPages.isPresent()) {
                buildPages = nestedLoopJoinPages.get().getPages();
            }
        }
        return buildPages != null;
    }