presto-main/src/main/java/io/prestosql/operator/AssignUniqueIdOperator.java/AssignUniqueIdOperator/AssignUniqueIdOperator
class AssignUniqueIdOperator:    public AssignUniqueIdOperator(OperatorContext operatorContext, AtomicLong rowIdPool)
    {
        this.operatorContext = requireNonNull(operatorContext, "operatorContext is null");
        this.rowIdPool = requireNonNull(rowIdPool, "rowIdPool is null");

        TaskId fullTaskId = operatorContext.getDriverContext().getTaskId();
        uniqueValueMask = (((long) fullTaskId.getStageId().getId()) << 54) | (((long) fullTaskId.getId()) << 40);

        requestValues();
    }