Swift Concurrency by Example
Swift Concurrency by Example walks you through the many and varied ways of running concurrent code in Swift, including async/await, tasks, actors, and more.
Introduction
- This stuff is hard
- How to follow this guide
- Concurrency vs parallelism
- Understanding threads and queues
- Main thread and main queue: what’s the difference?
- Where is Swift concurrency supported?
- Dedication
Async/await
- What is a synchronous function?
- What is an asynchronous function?
- How to create and call an async function
- How to call async throwing functions
- What calls the first async function?
- What’s the performance cost of calling an async function?
- How to create and use async properties
- How to call an async function using async let
- What’s the difference between await and async let?
- Why can’t we call async functions using async var?
- How to use continuations to convert completion handlers into async functions
- How to create continuations that can throw errors
- How to store continuations to be resumed later
- How to fix the error “async call in a function that does not support concurrency”
Sequences and streams
- What’s the difference between Sequence, AsyncSequence, and AsyncStream?
- How to loop over an AsyncSequence using for await
- How to manipulate an AsyncSequence using map(), filter(), and more
- How to create a custom AsyncSequence
- How to convert an AsyncSequence into a Sequence
Tasks and task groups
- What are tasks and task groups?
- How to create and run a task
- What’s the difference between a task and a detached task?
- How to get a Result from a task
- How to control the priority of a task
- Understanding how priority escalation works
- How to cancel a Task
- How to make a task sleep
- How to voluntarily suspend a task
- How to create a task group and add tasks to it
- How to cancel a task group
- How to handle different result types in a task group
- What’s the difference between async let, tasks, and task groups?
- How to make async command-line tools and scripts
- How to create and use task local values
- How to run tasks using SwiftUI’s task() modifier
- Is it efficient to create many tasks?
Actors
- What is an actor and why does Swift have them?
- How to create and use an actor in Swift
- How to make function parameters isolated
- How to make parts of an actor nonisolated
- How to use @MainActor to run code on the main queue
- Understanding how global actor inference works
- What is actor hopping and how can it cause problems?
- What’s the difference between actors, classes, and structs?
- Important: Do not use an actor for your SwiftUI data models
Solutions
