Returns the global system queue with the specified quality-of-service class.
- iOS 8.0+
- macOS 10.10+
- Mac Catalyst 13.0+Beta
- tvOS 9.0+
- watchOS 2.0+
- Xcode 6.0.1+
The quality-of-service level to associate with the queue. This value determines the priority at which the system schedules tasks for execution. For a list of possible values, see
Qo S .Qo SClass
This method returns a queue suitable for executing tasks with the specified quality-of-service level. Calls to the
dispatch functions have no effect on the returned queues.
Tasks submitted to the returned queue are scheduled concurrently with respect to one another.