Concurrency
Dive deep into Swift’s latest concurrency changes, covering async-await, actors, and more.
@preconcurrency: Incremental migration to concurrency checking
The @preconcurrency attribute is part of the tools that help you incrementally migrate to strict concurrency checking. When async/await was introduced by Apple, we were writing non-structured asynchronous code, mainly using closures. On our road to Swift 6, we must prepare our projects for strict concurrency checks done by the ...
Detached Tasks in Swift explained with code examples
Detached tasks allow you to create a new top-level task and disconnect from the current structured concurrency context. You could argue that using them results in unstructured concurrency since you're disconnecting potentially relevant tasks. While it sounds terrible to disconnect from structured concurrency, there are still examples of use cases ...
Task Groups in Swift explained with code examples
Task Groups in Swift allow you to combine multiple parallel tasks and wait for the result to return when all tasks are finished. They are commonly used for tasks like combining multiple API request responses into a single response object. Read my article about tasks first if you're new to ...
Sendable and @Sendable closures explained with code examples
Sendable and @Sendable are part of the concurrency changes that arrived in Swift 5.5 and address a challenging problem of type-checking values passed between structured concurrency constructs and actor messages. Before diving into the topic of sendables, I encourage you to read up on my articles around async/await, actors, and ...
AsyncSequence explained with Code Examples
AsyncSequence is part of the concurrency framework and the SE-298 proposal. Its name implies it's a type providing asynchronous, sequential, and iterated access to its elements. In other words: it's an asynchronous variant of the regular sequence we're familiar with in Swift. Like you won't often create your custom Sequence ...
AsyncThrowingStream and AsyncStream explained with code examples
AsyncThrowingStream and AsyncStream are part of the concurrency framework introduced in Swift 5.5 due to SE-314. Async streams allow you to replace existing code that is based on closures or Combine publishers. Before diving into details around throwing streams, I recommend reading my article covering async-await if you didn't do ...
Tasks in Swift explained with code examples
Tasks in Swift are part of the concurrency framework introduced at WWDC 2021. A task allows us to create a concurrent environment from a non-concurrent method, calling methods using async/await. When working with tasks for the first time, you might recognize familiarities between dispatch queues and tasks. Both allow dispatching ...
Nonisolated and isolated keywords: Understanding Actor isolation
SE-313 introduced the nonisolated and isolated keywords as part of adding actor isolation control. Actors are a new way of providing synchronization for shared mutable states with the new concurrency framework. If you're new to actors in Swift, I encourage you to read my article Actors in Swift: how to ...
Async let explained: call async functions in parallel
Async let is part of Swift's concurrency framework and allows instantiating a constant asynchronously. The concurrency framework introduced the concept of async-await, which results in structured concurrency and more readable code for asynchronous methods. If you're new to async-await, it's recommended first to read my article Async await in Swift ...
Actors in Swift: how to use and prevent data races
Swift Actors are new in Swift 5.5 and are part of the big concurrency changes at WWDC 2021. Before actors, data races were a common exception to run into. So before we dive into Actors with isolated and nonisolated access, it's good to understand what Data Races are and to ...
