Can you explain what is meant by quality of service in systems?

Quality of Service (QoS) in systems is a set of characteristics that define the level of reliability, availability, and performance of a service.

In the context of iOS applications, QoS often relates to task execution priorities, affecting resource allocation and response time. For example, high-QoS tasks are executed faster and with higher priority than background tasks.

Example of QoS usage in iOS:

DispatchQueue.global(qos: .userInitiated).async {
    // High priority task, e.g., UI update
}

DispatchQueue.global(qos: .background).async {
    // Background task, e.g., data loading
}

Thus, QoS helps manage app performance and responsiveness, providing a better user experience.