swift-concurrency-patterns

name	swift-concurrency-patterns
description	Structured concurrency and thread safety patterns in modern Swift.
activation	Load when writing async/await code, actors, or concurrent Swift code

Skill: swift-concurrency-patterns

Overview

Structured concurrency and thread safety patterns in modern Swift.

async/await

• Prefer async/await over GCD (DispatchQueue).
• Legacy GCD only when bridging old completion-handler APIs.

Task and TaskGroup

• Use Task for fire-and-forget async work.
• Use TaskGroup for parallel collections of work.
• Use await for sequential dependencies.

Actors

• Use actor for mutable shared state accessed from multiple tasks.
• Mark non-actor-isolated methods with nonisolated only when thread-safe by design.
• Prefer @MainActor for UI-updating code.

Sendable

• Ensure types crossing actor boundaries conform to Sendable.
• Use @unchecked Sendable only as a last resort with documented justification.

Cancellation

• SwiftUI .task is cancellable by default when the view disappears.
• Check Task.isCancelled in long-running loops.
• Propagate cancellation to child tasks and network requests.

Continuations

• Use withCheckedContinuation / withCheckedThrowingContinuation only for bridging legacy completion-handler APIs to async/await.