stageswhile

Stageswhile is a control construct used to coordinate staged processing with a looping condition. It combines concepts from multi-stage programming and ordinary while loops by organizing work into a set of stages that may depend on the outcomes of other stages.

In a stageswhile model, each stage represents a unit of work with defined prerequisites. The construct repeatedly selects and executes all currently ready stages while a loop condition remains true or while progress is possible. After each iteration, the status of stages is updated; if no new work is possible and the condition still holds, the loop may halt to avoid deadlock.

Scheduling may be deterministic, following a fixed order of stages, or parallel, allowing independent stages to run concurrently. Some implementations require topological ordering to respect dependencies, while others use dataflow techniques to maximize parallelism.

Common applications include data processing pipelines, build systems, and ETL workflows, where stages model steps such as parsing, validation, transformation, and output. Stageswhile helps express iterative progression through a directed acyclic graph of tasks while honoring dependencies.

Advantages include clear representation of staged dependencies and built-in deadlock detection when no progress is possible. Limitations include potential for deadlock, increased scheduling complexity, and the need for careful specification of stage prerequisites and termination conditions.

See also: staged computation, dataflow programming, workflow orchestration, while loop.