Close the lost-wakeup gap between predicate and sleep
A producer signals just before a worker begins waiting; queued work then sleeps until another submission arrives.
- Focused work estimate
- 2h 30m + prerequisites
- Priority in the scenario
- Medium
- Engineering practice
- Condition variables · Happens-before · Concurrency testing
Estimated field mix
- Systems programming65%
- Quality engineering35%
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
- Workers test the queue predicate under the same synchronization boundary as waiting
- Spurious wakeups preserve correctness
- One job is claimed by one worker
Implementation constraints
- Document the predicate, mutex, and notification order in code comments beside the wait loop.
Verification to include
- Exercise enqueue before, during, and after worker wait.
- Force the historical interleaving and prove the queued job completes without a second signal.
Deliverables
- Correct wait loop and deterministic lost-wakeup test
Rollout and recovery
Run the old and new pools against the same scheduler trace before switching.
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.