Can you list and describe the main priority levels of QoS?

In iOS, QoS (Quality of Service) defines the priority of task execution in the system, affecting resource allocation and response time. The main QoS levels:

1. User-interactive — the highest priority. Used for tasks that require immediate interaction with the user (animations, input processing). Tasks should be executed as quickly as possible.

2. User-initiated — high priority for tasks started by the user that are expected to complete quickly (loading data upon user request).

3. Default — the default level, used if no other priority is specified.

4. Utility — low priority for long-running tasks that do not require immediate results (file downloads, synchronization).

5. Background — the lowest priority, for tasks that are not visible to the user and can run in the background (indexing, backup).

Example of creating a task with a specific QoS:

DispatchQueue.global(qos: .userInitiated).async {
    // Code for high-priority task
}

Proper use of QoS levels helps optimize application performance and responsiveness.