swift-concurrency

Swift Concurrency

Treat isolation and cancellation as API contracts. Compile under the project's real Swift language and strict-concurrency settings.

Core rules

• Prefer structured child tasks and task groups. Detached tasks require an explicit ownership and context-transfer justification.
• Keep mutable shared state actor-isolated or otherwise synchronized; do not silence diagnostics with unchecked Sendable without proof.
• Propagate cancellation through loops, AsyncSequence production, continuations, and I/O adapters.
• Resume checked continuations exactly once on every path; retain cancellation handles for callback APIs.
• Do not block cooperative executors with synchronous I/O or locks held across suspension.
• Preserve actor isolation in public protocols and closures. Use @MainActor only for UI/main-thread state, not as a general race workaround.
• Define ordering, buffering, backpressure, termination, and cleanup for AsyncStream/AsyncSequence adapters.
• Treat task-local values and priorities as contextual hints, not durable business state.

Review sequence

1. Map task creation to owners and termination conditions.
2. Trace actor isolation and Sendable crossings.
3. Trace cancellation from caller to resources and continuations.
4. Identify blocking work, unbounded buffers, reentrancy assumptions, and priority inversions.
5. Add deterministic lifecycle tests using clocks, continuations, or event-driven coordination.
6. Run strict-concurrency compilation and stress the affected state transitions.

swift build
swift test