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How to use a Background Thread in Swift?
In this article, you will learn how you can perform a task in the background using a background thread in the Swift language.
Swift provides us with several ways to perform background tasks. One popular option of theirs is GCD (generally called Grand Central Dispatch), which is a low-level API for managing concurrently in the Swift language.
The GCD provides us with a global queue for creating background threads. You can invoke the DispatchQueue.global() method to get an instance of a global dispatch queue. Using the same instance, you can use the async() method to execute a block of code asynchronously on that queue.
Syntax
Here is the syntax of how to use GCD to create a background thread −
DispatchQueue.global().async {
// This block of code will be executed in the background
// Perform some tasks here
}
This is the basic syntax of using DispatchQueue to execute async tasks.
DispatchQueue provides us with the ability to assign a priority to an action. For this, you can use the quality of service (QoS) class for the global queue, which determines the priority of the task.
GCD provides the following QoS classes −
.userInteractive − Tasks in this class are intended for tasks that need to be completed immediately in order to provide a responsive user interface. Those tasks are run on the main thread with the highest priority.
.userInitiated − Tasks in this class are intended for tasks that are initiated by the user and require a high level of performance. These tasks are run on a high-priority thread, and their priority is higher than tasks in the .default class.
.default − Tasks in this class are intended for tasks that are not time-critical and do not require a high level of performance. These tasks are run on a low-priority thread, and their priority is lower than tasks in the .userInitiated class.
.utility − Tasks in this class are intended for tasks that may take a long time to complete and do not require a high level of performance. These tasks are run on a low-priority thread, and their priority is lower than tasks in the .default class.
.background − Background tasks have the lowest priority of all tasks. Assign this class to tasks or dispatch queues that you use to perform work while your app is running in the background.
How to use a background thread to perform a task?
DispatchQueue.global(qos: .background).async {
// write code to perform a task in the background
}
When you use background threads, remember that they have the lowest priority of all threads. So perform your tasks carefully.
Conclusion
This is the most important thing in an iOS application as many times you need to perform some tasks in background threads. For example, you have to fetch the user's current location in the background thread, it will good option to use.
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