planifest Concurrency Patterns
Overview
Use this skill to choose concurrency mechanisms that preserve correctness under load and failure.
Scope Boundaries
- Use this skill when the task matches the trigger condition described in
description. - Do not use this skill when the primary task falls outside this skill's domain.
Inputs To Gather
- Shared state model and mutation frequency.
- Read/write patterns and contention expectations.
- Ordering, consistency, and latency requirements.
- Failure/timeout/retry semantics in concurrent flows.
Deliverables
- Selected concurrency pattern with rationale.
- Invariant and liveness assumptions.
- Risk list (race, deadlock, starvation, contention collapse).
- Verification plan (stress, race, soak, failure-injection tests).
Pattern Selection Cheatsheet
single-writer queue/actor: high contention mutable state.fine-grained lock: moderate contention with strict in-process consistency.lock-free/CAS: low-latency hot path with careful ABA/memory-ordering handling.immutable snapshot + swap: read-heavy workloads.idempotent async workflow: distributed coordination with retries.
Quick Example
- Problem: concurrent balance updates causing lost writes.
- Anti-pattern: read-modify-write without serialization.
- Safer options:
- single-writer actor per account,
- optimistic concurrency with version check + bounded retry.
Quality Standard
- Correctness invariants are explicit and testable.
- Deadlock/starvation prevention strategy is defined.
- Contention behavior is characterized at expected scale.
- Timeout/retry/cancellation behavior is deterministic.
- Selected pattern includes clear operational monitoring signals.
Workflow
- Define correctness invariants and liveness constraints.
- Map workload and contention profile.
- Compare candidate patterns with tradeoffs.
- Select pattern and define failure/timeout semantics.
- Define targeted stress/race test strategy.
Failure Conditions
- Stop when invariants cannot be preserved by selected pattern.
- Stop when deadlock or starvation risk is unbounded.
- Escalate when required throughput conflicts with safe coordination model.