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Devii · Mobile · 2026-04-24 · 8 min read

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Swift Structured Concurrency: async/await, Tasks, And Actors

Apple's concurrency model in Swift 5.5+ and later: cooperative threads, task cancellation, and actor isolation.

Swift added **structured concurrency** in Swift 5.5: `async` functions, `await` suspension points, and `Task` hierarchies where child tasks inherit cancellation and priority. Documentation lives on `docs.swift.org` and in Apple's Swift books.

**Actors** serialize access to mutable state within an actor instance, reducing data races without manual locks for typical UI and service code. `@MainActor` pins UI mutations to the main thread in UIKit and SwiftUI apps.

Team code review
Team code review

Bridging legacy completion-handler APIs uses `withCheckedContinuation`. Mixing GCD patterns with async code without discipline can reintroduce races; prefer incremental migration module by module.

On the server, Swift on Linux supports the same concurrency model in Vapor and other frameworks. Verify your deployment target Swift version matches dependencies built for it.