ios-concurrency

Async/await replaces callback-based code with sequential syntax. Convert completion handlers by making functions `async` and using `await` instead of callbacks, improving readability and eliminating callback nesting.

Data races occur when multiple tasks access shared mutable state unsafely. Fix them by using actors to isolate state, conforming types to `Sendable`, and applying `@MainActor` for UI-bound code.

`@MainActor` ensures code runs on the main thread for UI updates; actor isolation protects data access across any thread. Use `@MainActor` for view controllers and UI logic, actors for general concurrency safety.

Freezing typically occurs when long-running tasks block the main thread. Move heavy work off the main thread using background actors or Task.detached, and ensure UI updates return to the main thread with `@MainActor`.

Sendable marks types as safe to pass between isolated concurrency domains. It's required for parameters and return values crossing actor boundaries; implement it by ensuring all stored properties are Sendable.

Migrate by replacing callbacks with async/await, adding Sendable conformance to shared types, isolating mutable state in actors, and applying `@MainActor` to UI code. Address compiler warnings incrementally.