  The OpenMP API offers both task-based and data-parallel concepts to
scientific computing. While it provides descriptive and prescriptive
annotations, it is in many places deliberately unspecific how to implement its
annotations. As the predominant OpenMP implementations share design rationales,
they introduce "quasi-standards how certain annotations behave. By means of a
task-based astrophysical simulation code, we highlight situations where this
"quasi-standard" reference behaviour introduces performance flaws. Therefore,
we propose prescriptive clauses to constrain the OpenMP implementations.
Simulated task traces uncover the clauses' potential, while a discussion of
their realization highlights that they would manifest in rather incremental
changes to any OpenMP runtime supporting task priorities.
