taskswhile

Taskswhile is a term used in discussions of concurrent programming to describe a pattern in which a collection of tasks is executed while a controlling condition remains true. It is not a formal language construct in most programming languages, but rather a design pattern that combines elements of a while loop with asynchronous task scheduling. The intent is to drive work by continuously evaluating a condition and dispatching tasks that perform units of work, often with the ability to cancel or await completion when the condition changes.

Semantics: The pattern typically begins by evaluating a condition. If true, it schedules one or more tasks and proceeds to monitor their completion or cancellation status. The loop continues while the condition holds, potentially spawning new tasks in each iteration or maintaining a pool of worker tasks with bounded concurrency. When the condition becomes false, in most implementations outstanding tasks are signaled to stop and the system waits for tasks to terminate or cancels them if supported.

Variants: Common variants include 1) unbounded taskswhile, which may spawn new tasks indefinitely, and 2) bounded taskswhile, which limits concurrent tasks with a semaphore or pool. Some implementations use cancellation tokens, futures, or promises to coordinate stopping.

Example: Pseudo-code: while (condition) { if (canSpawn()) schedule(doWork()); } where doWork checks for cancellation and performs a unit of work. And a bounded variant uses a semaphore to cap concurrent tasks.

Use cases: Data streaming, long-running batch processes, and responsive systems that must continue processing while a runtime condition remains true. Considerations include error handling, backpressure, cancellation semantics, and ensuring termination.

See also: asynchronous programming, task-based parallelism, cancellation tokens.