Capture a concurrency failure without megabytes of logs
A rare stall produces per-poll logs from every worker, changing timing and obscuring the last useful state transition.
- Focused work estimate
- 6h + prerequisites
- Priority in the scenario
- High
- Engineering practice
- Diagnostics · Ring buffers · Privacy
Estimated field mix
- Systems programming65%
- Site reliability35%
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.
- SCONCUR-102 · Reject work when the bounded queue is full
- SCONCUR-101 · Define queue ownership before starting worker threads
- SCONCUR-103 · Close the lost-wakeup gap between predicate and sleep
- SCONCUR-104 · Keep cancellation distinct from successful completion
- SCONCUR-105 · Prevent priority work from starving maintenance forever
- SCONCUR-106 · Remove a lock-order inversion in completion reporting
Acceptance criteria
- Record a bounded ring of queue and worker transitions
- Events use monotonic sequence and synthetic job identity
- Snapshot identifies dropped diagnostic events
Implementation constraints
- Do not record job payloads, thread stack memory, or unbounded labels.
Verification to include
- Reconstruct a normal claim-to-completion path from the ring.
- Overflow the ring during the forced deadlock trace and retain an explicit loss marker.
Deliverables
- Bounded trace recorder and stall diagnostic
Rollout and recovery
Enable the recorder only for the local harness until overhead is measured.
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.