Concurrency Safety

Concurrency safety in Swift, particularly with the introduction of Swift 6, focuses on eliminating data races by ensuring data race safety at compile time. This is achieved through several mechanisms:

1. Data Race Safety by Default: In Swift 6, data race safety is enforced by default, turning potential data race issues into compile-time errors. This significantly enhances the security and reliability of applications by preventing runtime data races, which can lead to crashes and unpredictable behavior.

2. Actors and Sendable Protocol: Swift introduces actors, which are reference types that automatically protect their state by serializing access, allowing only one task to execute at a time. The Sendable protocol ensures that values shared between concurrency domains are safe, preventing concurrent access issues.

3. Low-Level Synchronization Primitives: Swift 6 includes new low-level primitives like atomics and mutexes for synchronization. Atomics provide efficient, lock-free implementations, while mutexes ensure mutually exclusive access to shared resources.

4. Incremental Migration and Concurrency Checking: Developers can incrementally adopt Swift 6's concurrency features. By enabling strict concurrency checking in Xcode 16, developers can identify and address concurrency issues in their codebase, even if some modules or libraries have not yet been updated to Swift 6.

For more detailed guidance on migrating to Swift 6 and adopting these concurrency features, you can refer to the session Migrate your app to Swift 6 (11:05) which discusses enabling complete checking in the watch extension.