Returns a system-defined global concurrent queue with the specified quality of service class.
- iOS 4.0+
- macOS 10.6+
- tvOS 9.0+
- watchOS 2.0+
The quality of service you want to give to tasks executed using this queue. Quality-of-service helps determine the priority given to tasks executed by the queue. You may specify the values
QOS_CLASS_BACKGROUND. Queues that handle user-interactive or user-initiated tasks have a higher priority than tasks meant to run in the background.
In OS X 10.9 or earlier, you can specify one of the dispatch queue priority values, which are found in Dispatch Queue Priorities. These values map to an appropriate quality-of-service class.
Flags that are reserved for future use. Always specify
0for this parameter.
The requested global concurrent queue.
This function returns a queue suitable for executing tasks with the specified quality-of-service level. Calls to the
dispatch_set_context functions have no effect on the returned queues.
Tasks submitted to the returned queue are scheduled concurrently with respect to one another.