Swift Concurrency Review

Swift concurrency review

Review concurrent Swift code in the consumer workspace. Prefer findings and a fix plan; change code only when the user authorized implementation.

Workflow

1. Map isolation. List actor boundaries (MainActor, custom actors), global/shared mutable state, and which types cross isolation. Note observation/@Observable objects and where UI reads them.
2. Structured concurrency first. Prefer async functions, task groups, and child tasks tied to a scope. Flag unstructured Task { } that outlives the caller without ownership; require a written reason for Task.detached.
3. Cancellation. Ensure long-running work checks cancellation (Task.checkCancellation / try Task.checkCancellation / cooperative exits) and that callers can cancel. Avoid swallowing CancellationError as success.
4. UI on the main actor. View updates, UIKit/AppKit bridging, and observable model mutations that drive UI should be main-actor isolated or explicitly hopped. Flag off-main UI mutation.
5. Sendable at boundaries. Resolve compiler diagnostics at isolation edges; avoid @unchecked Sendable unless the invariant is documented and enforced. Prefer value types or actor-owned state over shared classes.
6. Data races and reentrancy. Watch for mutable capture in concurrent closures, non-isolated mutable globals, and actor reentrancy assumptions (state may change across await).
7. Observation pitfalls. Avoid redundant observation that performs heavy work on every change; keep expensive async work explicit and cancellable when views disappear.
8. Findings format. For each issue: location, isolation problem, impact, recommended fix, and whether a test can lock it. Severity: blocking / should-fix / note.

Review-only vs fix

• Review-only: findings + recommended sequence; no product code changes.
• Authorized fixes: smallest isolation-correct change; add deterministic tests where practical.
• Do not use this skill for pure styling or synchronous API bikeshedding.

Verification

When code changes, use swift-testing-verification and a strict-concurrency-aware build when the project enables it. Report exact tools/commands and outcomes. Never claim a concurrency check passed without running it. List residual risk for untested race windows.

Inputs: concurrent code and compiler diagnostics when available. Output: a concurrency finding/fix set, deterministic tests where practical, and strict-concurrency build result. A review-only request does not change code.