Grand Central Dispatch (the OS-level framework that handles these QoS classes) elevates the priority of a queue if there is high priority work waiting on low pr

Grand Central Dispatch (the OS-level framework that handles these QoS classes) elevates the priority of a queue if there is high priority work waiting on low priority work to finish. https://developer.apple.com/library/archive/documentation/Performance/Conceptual/EnergyGuide-iOS/PrioritizeWorkWithQoS.html#//apple_ref/doc/uid/TP40015243-CH39-SW44 https://developer.apple.com/library/archive/documentation/Pe...