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.
THIS IS AN EARLY, INCOMPLETE EDITION OF THE BOOK.
Many more chapters will be added in the next four to six weeks, along with extra examples and more detail in the existing chapters, plus downloadable Xcode projects and illustrations to help make concepts clearer.
All the code in this book requires Xcode 13.0 or later.
Thank you for your patience! If you spot any problems with the text, please email paul@hackingwithswift.com.
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
