There are the following categories of QoS classes present in the system.
User Interactive : When we launch an application in iOS, to get a nice user experience, we need some tasks to be executed immediately. Such tasks are user interactive, which are to be executed for nice user experience. As a developer, we must use these tasks for UI Updates, event handling, and small workloads. The user-interactive tasks need to be executed on the main thread.
User-Initiated : These tasks are initiated by the user from the user interface. These are asynchronous tasks that are to be used when the user waits in the application for immediate results, such as some API calls. The user-initiated tasks are executed in the high priority global queue.
Utility : these are long-running tasks that run typically with a progress indicator. These types of threads are used for networking, computations, I/O, etc. These tasks are executed in the low priority global queue.
