WWDC23 SALE: Save 50% on all my Swift books and bundles! >>

What are tasks and task groups?

Paul Hudson    @twostraws   

Updated for Xcode 14.2

Using async/await in Swift allows us to write asynchronous code that is easy to read and understand, but by itself it doesn’t enable us to run anything concurrently – even with several CPU cores working hard, async/await code would still execute sequentially.

To create actual concurrency – to provide the ability for multiple pieces of work to run at the same time – Swift provides us with two specific types for constructing and managing concurrency in a way that makes it easier to use: Task and TaskGroup. Although the types themselves aren’t complex, they unlock a lot of power and flexibility, and sit at the core of how we use concurrency with Swift.

Which you choose – Task or TaskGroup – depends on the goal of your work: if you want one or two independent pieces of work to start, then Task is the right choice. If you want to split up one job into several concurrent operations then TaskGroup is a better fit. Task groups work best when their individual operations return exactly the same kind of data, but with a little extra effort you can coerce them into supporting heterogenous data types.

Although you might not realize it, you’re using tasks every time you write any async code in Swift. You see, all async functions run as part of a task whether or not we explicitly ask for it to happen. Even using async let is syntactic sugar for creating a task then waiting for its result – special syntax that makes a particular piece of code easier to write. This is why if you use multiple sequential async let calls they will all start executing immediately while the rest of your code continues.

Both Task and TaskGroup can be created with one of four priority levels: high is the most important, then medium, low, and finally background at the bottom. Task priorities allow the system to adjust the order in which it executes work, meaning that important work can happen before unimportant work.

Tip: If you’ve been doing iOS programming for a while, you may prefer to use the more familiar quality of service priorities from DispatchQueue, which are userInitiated and utility in place of high and low respectively. There is no equivalent to the old userInteractive priority, which is now exclusively reserved for the user interface.

Save 50% in my WWDC23 sale.

SAVE 50% To celebrate WWDC23, all our books and bundles are half price, so you can take your Swift knowledge further without spending big! Get the Swift Power Pack to build your iOS career faster, get the Swift Platform Pack to builds apps for macOS, watchOS, and beyond, or get the Swift Plus Pack to learn advanced design patterns, testing skills, and more.

Save 50% on all our books and bundles!

Similar solutions…

Buy Pro Swift Buy Pro SwiftUI Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let us know!

Average rating: 4.0/5

Unknown user

You are not logged in

Log in or create account

Link copied to your pasteboard.