KITFORMA · EDITORIAL ANSWER
Why does a CPU-heavy operation inside an async Tokio task stall other tasks?
KitForma editorial guide. An async task does not yield simply because its function is declared async. Long synchronous computation can occupy an executor worker without reaching a cooperative suspension point.
Step-by-step answer
An async task does not yield simply because its function is declared async. Long synchronous computation can occupy an executor worker without reaching a cooperative suspension point.
Use an appropriate bounded CPU pool or spawn_blocking for suitable blocking work, with a deliberate concurrency limit. Avoid scheduling unbounded heavy jobs onto its comparatively permissive blocking capacity. Pass owned input and report completion/error explicitly.
Run a periodic lightweight task beside a synthetic heavy operation to check responsiveness. Once blocking work starts, aborting its join handle generally cannot forcibly stop it; design cooperative cancellation inside long-running computations when needed. Moving work off the executor is not a memory or workload quota by itself.
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