main thread hangs
Asked on 06/16/2025
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If you're experiencing main thread hangs, it might be due to expensive operations being executed on the main thread, which can block UI updates and lead to a poor user experience. At WWDC, Apple presented several sessions that address this issue by leveraging Swift concurrency to improve app performance.
In the session Code-along: Elevate an app with Swift concurrency, it was demonstrated how to move expensive image processing tasks to a background thread to prevent blocking the main thread. This ensures that the main thread remains responsive to UI events, such as scrolling gestures.
Additionally, the session Embracing Swift concurrency discussed the importance of using asynchronous tasks to offload work from the main thread. This session highlighted the use of profiling tools like Instruments to identify performance bottlenecks and determine which tasks can be moved to background threads.
By adopting these concurrency techniques, you can significantly reduce main thread hangs and improve the responsiveness of your app.
Code-along: Elevate an app with Swift concurrency
Learn how to optimize your app’s user experience with Swift concurrency as we update an existing sample app. We’ll start with a main-actor app, then gradually introduce asynchronous code as we need to. We’ll use tasks to optimize code running on the main actor, and discover how to parallelize code by offloading work to the background. We’ll explore what data-race safety provides, and work through interpreting and fixing data-race safety errors. Finally, we’ll show how you can make the most out of structured concurrency in the context of an app.
Embracing Swift concurrency
Join us to learn the core Swift concurrency concepts. Concurrency helps you improve app responsiveness and performance, and Swift is designed to make asynchronous and concurrent code easier to write correctly. We’ll cover the steps you need to take an app through from single-threaded to concurrent. We’ll also help you determine how and when to make the best use of Swift concurrency features – whether it’s making your code more asynchronous, moving it to the background, or sharing data across concurrent tasks.
What’s new in Xcode 16
Discover the latest productivity and performance improvements in Xcode 16. Learn about enhancements to code completion, diagnostics, and Xcode Previews. Find out more about updates in builds and explore improvements in debugging and Instruments.