Time Consuming Task in Background Thread in Swift

In this tutorial, you will learn how to perform a time-consuming task in a background thread in Swift. In iOS development, achieving concurrency primarily involves effectively utilizing multi-threading. Running multiple threads can give the appearance of simultaneous execution, which is crucial for keeping the UI responsive while performing heavy computations or network requests.

Why Background Tasks are Needed for Swift & iOS Applications

Background tasks are essential for Swift and iOS applications due to the nature of the mobile platform. Mobile devices often have limited resources compared to desktop computers, especially in terms of CPU power and memory. Running intensive tasks on the main thread can lead to unresponsive UI and poor user experience.

So, you can move time-consuming tasks to a background thread. It allows the main thread to remain free to respond to user interactions, thus keeping the application fluid and responsive.

1. Background Task with Grand Central Dispatch (GCD)

One way of executing a background task is to use Grand Central Dispatch (GCD). GCD is a tool that helps you manage and schedule tasks in your iOS app, allowing you to execute code concurrently.

Here’s an example of how you can use GCD to perform a task in the background:

DispatchQueue.global(qos: .background).async {
   // Your long-running task here

   DispatchQueue.main.async {
       // Any UI updates go here

In this code snippet, the global(qos: .background) method schedules the task on a background thread. The async method then schedules the task to be run asynchronously. You are facing user data from the internet using getUserData() and once the task is complete, any UI updates are scheduled to be performed on the main thread using the updateUserInfo() function.

Also, you can use several types of dispatch queues to handle different levels of priority:

  • DispatchQueue.main: Main thread. Used for UI-related tasks.
  • DispatchQueue.global(qos: .userInitiated): High priority. Useful for tasks initiated by the user.
  • DispatchQueue.global(qos: .userInteractive): High priority. Similar to .userInitiated, but slightly lower.
  • DispatchQueue.global(qos: .background): Lowest priority. Useful for tasks that don’t require immediate attention.
  • DispatchQueue.global(qos: .default): Normal priority. After high but before low.
  • DispatchQueue.global(qos: .utility): Low priority. Useful for tasks that can be performed in the background.
  • DispatchQueue.global(qos: .unspecified): Absence of quality. Used when no specific quality class is desired.

However, GCD can be verbose and complex for complex concurrency scenarios.

2. Background Task with async/await: A Modern Way

With the introduction of Swift 5.5, Apple has introduced new concurrency primitives like async/await and actors. These provide a more modern and streamlined way to manage concurrency in Swift.

Here’s an example of how you can use async/await to perform a task in the background:

func handleSignUp() async {
    // Time consuming tasks

Task {
    await handleSignUp()

In this code snippet, the Task initializer schedules the task to be run asynchronously for handling signup. Unlike GCD, async/await provides a simpler and more intuitive syntax for managing concurrency. Also, async/await simplifies asynchronous code, improving readability and conciseness. To learn more about async/await check the official documentation for concurrency provided by Apple.

The code example above demonstrates how to manage user sign-up using Task and async/await. The handleSignUp() method makes a network request in the background, and when it fetches the response, it updates the UI according to the result.


In conclusion, executing time-consuming tasks on background threads is a critical aspect of iOS development. While GCD is a powerful tool for managing concurrency, Swift’s newer concurrency features provide a more modern and streamlined approach. However, Apple provides some limits for using background tasks. You can check this forum post iOS Background execution limits.

For more Swift Code examples and tutorials, please check the Swift Code Examples page on this website.

Happy Coding!

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