swift-concurrency

Swift Structured Concurrency

Pattern catalog for Swift's structured concurrency model: async/await, Actors, TaskGroups, AsyncSequence, Sendable, and cancellation. Load the reference file matching the developer's question.

Reference Loading Table

| Signal | Reference File | Content | |--------|---------------|---------| | async/await, Task, Sendable | references/fundamentals.md | async/await patterns, Task/Task.detached, Sendable/@Sendable | | Actor, @MainActor, nonisolated | references/actor-isolation.md | Actor isolation, MainActor UI confinement, nonisolated opt-out | | TaskGroup, AsyncSequence, AsyncStream, cancellation | references/task-patterns.md | Structured concurrency, rate-limited groups, streams, cancellation | | Failure modes, common mistakes | references/preferred-patterns.md | Blocking MainActor, task leaking, actor reentrancy hazard |

Key Conventions

• Prefer structured concurrency -- use TaskGroup over loose Task { } whenever possible; structured tasks propagate cancellation and errors automatically.
• Mark types Sendable -- enable strict concurrency checking (-strict-concurrency=complete) and resolve all warnings before they become errors in Swift 6.
• Use actors for shared mutable state -- avoid manual locks; actors provide compiler-verified safety.
• Cancel what you create -- every Task stored in a property should have a corresponding cancellation path.
• Minimize @MainActor surface -- isolate only the UI layer; keep business logic and networking off the main actor.

References

• references/fundamentals.md -- async/await, Task, Sendable basics
• references/actor-isolation.md -- Actor, @MainActor, nonisolated
• references/task-patterns.md -- TaskGroup, AsyncSequence, AsyncStream, cancellation
• references/preferred-patterns.md -- blocking, leaking, reentrancy mistakes