- iOS 4.3+
- macOS 10.7+
- tvOS 9.0+
- watchOS 2.0+
Items dispatched to the queue run at background priority; the queue is scheduled for execution after all high priority queues have been scheduled and the system runs items on a thread whose priority is set for background status. Such a thread has the lowest priority and any disk I/O is throttled to minimize the impact on the system.
This constant maps to the QOS_CLASS_BACKGROUND class.