Keep cancellation distinct from successful completion
A cancelled indexing job resolves the same completion channel as a finished job, so callers publish an empty index.
- Focused work estimate
- 2h 30m + prerequisites
- Priority in the scenario
- Medium
- Engineering practice
- Cancellation · State modeling
Estimated field mix
- Systems programming70%
- Real-time systems30%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional image-indexing utility runs CPU-only synthetic jobs through a Rust worker pool. Its prototype loses wakeups, blocks shutdown, and treats cancellation as completion. Build a local library and deterministic concurrency harness; image content, GPU work, and production deployment are excluded.
Setup prerequisites
- Mutexes and condition variables
- Atomics
- Thread lifecycle
Preceding work
Complete these dependencies, or supply their agreed outputs before taking this ticket.
Acceptance criteria
- Result distinguishes success, cancellation, job failure, and pool shutdown
- Cancellation before claim prevents execution
- Cancellation after claim is cooperative and observable
Implementation constraints
- Do not terminate worker threads asynchronously while they own locks or memory.
Verification to include
- Cancel queued and running cooperative jobs and inspect distinct outcomes.
- Use a job that ignores cancellation and verify shutdown reports the unresolved work.
Deliverables
- Cancellation state model and race tests
Rollout and recovery
Callers must handle cancellation explicitly before adopting the new result type.
Value of the work
For the engineer: Practice happens-before reasoning, ownership transfer, cancellation and liveness testing.
For the team: Review a worker primitive whose overload and shutdown behavior are predictable before it supports build or media workloads.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.