Characterize whether quiescent fairness implies Tokio fairness

Determine whether there exists a quiescently fair scheduler that is not Tokio fair, thereby characterizing the relationship between quiescent fairness and the bounded-delay fairness notion defined for Tokio schedulers.

Background

The paper proves that a quiescently fair scheduler equipped with a suitable well-founded scheduling-distance measure and a bounded distance is also Tokio fair. This establishes one implication between the two fairness notions.

The converse is explicitly left unresolved: the paper does not determine whether the class of quiescently fair schedulers strictly contains the class of Tokio-fair schedulers. Resolving this would clarify whether Tokio fairness is strictly weaker than quiescent fairness or whether the two notions coincide under some conditions.

References

It is unknown whether there exist any quiescent fair schedulers that are not Tokio fair.

— A Complete, Formal Semantics for Rust Source Code  (2610.06003 - Drodt, 5 Oct 2026) in Appendix C, “Relation of Quiescent and Tokio Fairness,” immediately after Corollary C.1