{ "policy": { "version": 5, "patterns": { "version": 1, "method": "CURATED_PRACTICE_TOPIC", "notice": "Pattern topics identify design choices to practice. Read the ticket's acceptance criteria and justify the simplest suitable approach. Tags are not capability or ownership evidence; an untagged ticket has no curated pattern topic assigned." }, "fieldMix": { "version": 1, "method": "CURATED_ESTIMATE", "notice": "Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence." }, "contentStatus": "PRACTICE_BRIEF", "assessmentStatus": "NOT_QUALIFIED", "evidenceUse": "NONE", "aiPolicy": "AI tools are welcome during implementation. Record assumptions, review the result, and verify its behavior.", "notice": "Fictional engineering practice briefs. Starter repositories, fixtures, automated grading, and verified ownership are not included.", "outcomeEvidence": "Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.", "ownershipEvidence": "Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence." }, "patternTopics": [ { "id": "factory-method", "label": "Factory Method", "group": "Creational" }, { "id": "abstract-factory", "label": "Abstract Factory", "group": "Creational" }, { "id": "builder", "label": "Builder", "group": "Creational" }, { "id": "prototype", "label": "Prototype", "group": "Creational" }, { "id": "singleton", "label": "Singleton", "group": "Creational" }, { "id": "adapter", "label": "Adapter", "group": "Structural" }, { "id": "bridge", "label": "Bridge", "group": "Structural" }, { "id": "composite", "label": "Composite", "group": "Structural" }, { "id": "decorator", "label": "Decorator", "group": "Structural" }, { "id": "facade", "label": "Facade", "group": "Structural" }, { "id": "flyweight", "label": "Flyweight", "group": "Structural" }, { "id": "proxy", "label": "Proxy", "group": "Structural" }, { "id": "chain-of-responsibility", "label": "Chain of Responsibility", "group": "Behavioral" }, { "id": "command", "label": "Command", "group": "Behavioral" }, { "id": "interpreter", "label": "Interpreter", "group": "Behavioral" }, { "id": "iterator", "label": "Iterator", "group": "Behavioral" }, { "id": "mediator", "label": "Mediator", "group": "Behavioral" }, { "id": "memento", "label": "Memento", "group": "Behavioral" }, { "id": "observer", "label": "Observer", "group": "Behavioral" }, { "id": "state", "label": "State", "group": "Behavioral" }, { "id": "strategy", "label": "Strategy", "group": "Behavioral" }, { "id": "template-method", "label": "Template Method", "group": "Behavioral" }, { "id": "visitor", "label": "Visitor", "group": "Behavioral" }, { "id": "ports-and-adapters", "label": "Ports and Adapters", "group": "Architectural" }, { "id": "cqrs", "label": "CQRS", "group": "Architectural" }, { "id": "strangler-fig", "label": "Strangler Fig", "group": "Architectural" }, { "id": "saga", "label": "Saga", "group": "Distributed and reliability" }, { "id": "transactional-outbox", "label": "Transactional Outbox", "group": "Distributed and reliability" }, { "id": "circuit-breaker", "label": "Circuit Breaker", "group": "Distributed and reliability" }, { "id": "bulkhead", "label": "Bulkhead", "group": "Distributed and reliability" } ], "projects": [ { "key": "SCONCUR", "title": "Make a native work queue survive real thread interleavings", "field": "Systems programming", "summary": "Implement bounded scheduling, cancellation and shutdown without hidden liveness failures.", "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.", "stack": [ "Rust", "Threads", "Loom or deterministic scheduler", "Criterion" ], "prerequisites": [ "Mutexes and condition variables", "Atomics", "Thread lifecycle" ], "developerValue": "Practice happens-before reasoning, ownership transfer, cancellation and liveness testing.", "companyValue": "Review a worker primitive whose overload and shutdown behavior are predictable before it supports build or media workloads.", "delivery": "Ten linked tickets across three phases. Use synthetic inputs and a local harness; provide source, focused tests, measurements where requested, and a recovery note.", "phases": [ { "id": "model", "title": "Establish the machine contract", "goal": "Make representation, ownership and failure boundaries explicit." }, { "id": "control", "title": "Control resources and concurrency", "goal": "Implement bounded behavior under realistic interleavings." }, { "id": "operate", "title": "Prove recovery and handoff", "goal": "Measure, diagnose and safely replace the component." } ], "tickets": [ { "id": "f7ca3509-29b6-4f65-99e1-3d7576662142", "key": "SCONCUR-101", "title": "Define queue ownership before starting worker threads", "type": "TASK", "priority": "MEDIUM", "difficulty": "FOUNDATIONAL", "estimateMinutes": 90, "phaseId": "model", "dependsOn": [], "scenario": "Workers borrow configuration from a stack-owned builder that disappears after start, while the queue handle can outlive the pool.", "acceptanceCriteria": [ "Pool-owned state outlives every worker", "Queue handles cannot submit after terminal shutdown", "Dropping the final handle has documented behavior" ], "implementationNotes": [ "Avoid leaked static references and process-wide mutable state." ], "verification": [ "Create, submit, join, and drop a pool repeatedly under a leak checker.", "Drop external handles in different orders and verify workers cannot access released state." ], "deliverables": [ "Ownership diagram and lifecycle tests" ], "rollout": "Keep the single-thread runner until lifecycle checks pass.", "skills": [ "Ownership", "Thread lifecycle" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "Developer tooling", "percentage": 30 } ], "patterns": [] }, { "id": "6643c73d-d80b-4f64-85fd-86aaeb056e16", "key": "SCONCUR-102", "title": "Reject work when the bounded queue is full", "type": "BUG", "priority": "MEDIUM", "difficulty": "FOUNDATIONAL", "estimateMinutes": 90, "phaseId": "model", "dependsOn": [], "scenario": "Producers append without limit while workers are paused, and the process consumes all available memory.", "acceptanceCriteria": [ "Capacity is explicit and positive", "Submission returns accepted, timed out, or closed", "A rejected job remains caller-owned" ], "implementationNotes": [ "Do not hide backpressure behind an unbounded overflow list." ], "verification": [ "Fill the queue, release one slot, and submit the next job.", "Keep workers paused and confirm memory and queue length remain bounded." ], "deliverables": [ "Bounded submission API and overload tests" ], "rollout": "Start with conservative capacity and surface rejections to the local caller.", "skills": [ "Backpressure", "API design" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "Performance engineering", "percentage": 30 } ], "patterns": [] }, { "id": "c19d2098-1bff-474d-bd87-1de398309af2", "key": "SCONCUR-103", "title": "Close the lost-wakeup gap between predicate and sleep", "type": "STORY", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 150, "phaseId": "model", "dependsOn": [ "SCONCUR-101", "SCONCUR-102" ], "scenario": "A producer signals just before a worker begins waiting; queued work then sleeps until another submission arrives.", "acceptanceCriteria": [ "Workers test the queue predicate under the same synchronization boundary as waiting", "Spurious wakeups preserve correctness", "One job is claimed by one worker" ], "implementationNotes": [ "Document the predicate, mutex, and notification order in code comments beside the wait loop." ], "verification": [ "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": "Run the old and new pools against the same scheduler trace before switching.", "skills": [ "Condition variables", "Happens-before", "Concurrency testing" ], "fieldMix": [ { "field": "Systems programming", "percentage": 65 }, { "field": "Quality engineering", "percentage": 35 } ], "patterns": [] }, { "id": "f3824461-238d-4078-b064-2ab8f7ce08aa", "key": "SCONCUR-104", "title": "Keep cancellation distinct from successful completion", "type": "CHORE", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 150, "phaseId": "control", "dependsOn": [ "SCONCUR-103" ], "scenario": "A cancelled indexing job resolves the same completion channel as a finished job, so callers publish an empty index.", "acceptanceCriteria": [ "Result distinguishes success, cancellation, job failure, and pool shutdown", "Cancellation before claim prevents execution", "Cancellation after claim is cooperative and observable" ], "implementationNotes": [ "Do not terminate worker threads asynchronously while they own locks or memory." ], "verification": [ "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": "Callers must handle cancellation explicitly before adopting the new result type.", "skills": [ "Cancellation", "State modeling" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "Real-time systems", "percentage": 30 } ], "patterns": [] }, { "id": "151ac8b4-f24b-452e-a4c5-1fb309e47eda", "key": "SCONCUR-105", "title": "Prevent priority work from starving maintenance forever", "type": "TASK", "priority": "HIGH", "difficulty": "ADVANCED", "estimateMinutes": 240, "phaseId": "control", "dependsOn": [ "SCONCUR-102", "SCONCUR-104" ], "scenario": "A continuous stream of interactive jobs keeps cache-maintenance tasks queued indefinitely.", "acceptanceCriteria": [ "Scheduling policy defines a bounded wait for every admitted class", "Interactive latency remains measured under mixed load", "Class selection is deterministic for a declared seed" ], "implementationNotes": [ "Do not claim fairness from average completion time; report per-class tail wait." ], "verification": [ "Replay a mixed workload and verify the declared service ratio.", "Saturate the interactive class and confirm maintenance still advances." ], "deliverables": [ "Fair scheduler policy, simulator, and latency report" ], "rollout": "Canary the policy in the synthetic workload and retain FIFO fallback.", "skills": [ "Scheduling", "Fairness", "Performance analysis" ], "fieldMix": [ { "field": "Systems programming", "percentage": 60 }, { "field": "Performance engineering", "percentage": 40 } ], "patterns": [] }, { "id": "ed040569-ec1e-4543-92d6-a7a6e43d8ea1", "key": "SCONCUR-106", "title": "Remove a lock-order inversion in completion reporting", "type": "BUG", "priority": "HIGH", "difficulty": "ADVANCED", "estimateMinutes": 240, "phaseId": "control", "dependsOn": [ "SCONCUR-103", "SCONCUR-104" ], "scenario": "The worker holds the queue lock while acquiring a result lock; the joining thread holds the result lock while closing the queue.", "acceptanceCriteria": [ "Declare a single lock order or remove nested acquisition", "Completion remains visible before join returns", "Shutdown cannot wait while holding a lock needed by workers" ], "implementationNotes": [ "Keep callbacks outside internal locks because caller code is untrusted by the synchronization design." ], "verification": [ "Complete and join jobs from several workers under the deterministic scheduler.", "Force the prior opposing acquisition order and verify progress." ], "deliverables": [ "Lock graph, refactor, and deadlock regression" ], "rollout": "Enable lock-wait diagnostics during the local transition.", "skills": [ "Deadlock analysis", "Lock ordering" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "Quality engineering", "percentage": 30 } ], "patterns": [] }, { "id": "797d56ef-bcbb-4353-be8d-6623e8c56f68", "key": "SCONCUR-107", "title": "Prove the atomic queue fast path has a safe memory order", "type": "STORY", "priority": "HIGH", "difficulty": "EXPERT", "estimateMinutes": 360, "phaseId": "control", "dependsOn": [ "SCONCUR-102", "SCONCUR-103" ], "scenario": "A lock-free experiment publishes a slot index before all job fields are visible, producing rare partially initialized reads on a weakly ordered target.", "acceptanceCriteria": [ "Every atomic operation has a stated synchronization role", "Publication makes complete job data visible before claim", "Wraparound cannot confuse a reused slot with an older generation" ], "implementationNotes": [ "Prefer the mutex implementation unless measured need and model checking justify the atomic path." ], "verification": [ "Model-check bounded producers, consumers, and slot reuse.", "Weaken the publication ordering in a mutation and ensure the model detects an invalid read." ], "deliverables": [ "Memory-order argument, model, and comparison with mutex path" ], "rollout": "Keep the atomic implementation disabled unless correctness and workload benefit are both demonstrated.", "skills": [ "Atomics", "Memory models", "Model checking" ], "fieldMix": [ { "field": "Systems programming", "percentage": 65 }, { "field": "Performance engineering", "percentage": 35 } ], "patterns": [] }, { "id": "4095442e-43f4-4c14-b085-d1f24c90f716", "key": "SCONCUR-108", "title": "Drain accepted jobs without hanging process shutdown", "type": "CHORE", "priority": "HIGH", "difficulty": "ADVANCED", "estimateMinutes": 240, "phaseId": "operate", "dependsOn": [ "SCONCUR-104", "SCONCUR-106" ], "scenario": "Shutdown closes submissions but waits forever for a worker blocked on an external test double that never returns.", "acceptanceCriteria": [ "Shutdown defines stop-accepting, drain, cancel, and terminal states", "A deadline reports unfinished job identities without detaching live threads", "Repeated shutdown calls return the same terminal outcome" ], "implementationNotes": [ "Use controlled local jobs; do not kill threads or the host process to simulate recovery." ], "verification": [ "Drain a pool whose jobs complete before the deadline.", "Block one job past the deadline and confirm bounded return with an unresolved record." ], "deliverables": [ "Shutdown protocol and stuck-job test" ], "rollout": "Callers keep the old process exit path until they handle unresolved shutdown results.", "skills": [ "Graceful shutdown", "Recovery", "State machines" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "Site reliability", "percentage": 30 } ], "patterns": [] }, { "id": "7d717d6a-c13b-4544-9463-3bbc2e2d619e", "key": "SCONCUR-109", "title": "Capture a concurrency failure without megabytes of logs", "type": "TASK", "priority": "HIGH", "difficulty": "EXPERT", "estimateMinutes": 360, "phaseId": "operate", "dependsOn": [ "SCONCUR-105", "SCONCUR-106" ], "scenario": "A rare stall produces per-poll logs from every worker, changing timing and obscuring the last useful state transition.", "acceptanceCriteria": [ "Record a bounded ring of queue and worker transitions", "Events use monotonic sequence and synthetic job identity", "Snapshot identifies dropped diagnostic events" ], "implementationNotes": [ "Do not record job payloads, thread stack memory, or unbounded labels." ], "verification": [ "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": "Enable the recorder only for the local harness until overhead is measured.", "skills": [ "Diagnostics", "Ring buffers", "Privacy" ], "fieldMix": [ { "field": "Systems programming", "percentage": 65 }, { "field": "Site reliability", "percentage": 35 } ], "patterns": [] }, { "id": "b40b5dbb-c01e-46b6-ab37-04516954d6b6", "key": "SCONCUR-110", "title": "Publish the worker-pool contract and benchmark limits", "type": "BUG", "priority": "MEDIUM", "difficulty": "INTERMEDIATE", "estimateMinutes": 150, "phaseId": "operate", "dependsOn": [ "SCONCUR-105", "SCONCUR-108", "SCONCUR-109" ], "scenario": "A build tool and a request server both plan to reuse the pool despite different fairness, blocking, and shutdown requirements.", "acceptanceCriteria": [ "Document supported job behavior and prohibited blocking assumptions", "Report throughput, queue wait, memory, and shutdown duration for declared workloads", "List cases where a runtime-native executor is preferable" ], "implementationNotes": [ "Do not generalize results beyond the recorded machine and workload profiles." ], "verification": [ "Reproduce one CPU-bound and one mixed-duration benchmark from a clean checkout.", "Run the unsupported permanently blocking job and confirm the guide predicts the outcome." ], "deliverables": [ "Contract, benchmark manifest, and adoption checklist" ], "rollout": "Require each adopter to select and verify a workload profile.", "skills": [ "Benchmarking", "Documentation", "Capacity planning" ], "fieldMix": [ { "field": "Systems programming", "percentage": 70 }, { "field": "Developer tooling", "percentage": 30 } ], "patterns": [] } ], "id": "26536d74-4837-4bde-ab64-3f13e1b2f2f8" } ] }