I see this warning when my app runs: Thread running at QOS_CLASS_USER_INTERACTIVE waiting on a lower QoS thread running at QOS_CLASS_DEFAULT. Investigate ways to avoid priority inversions This is true; I know what is going on. I'd like this other thread to have a higher priority. But how do I set the "QOS class" for a thread? Searching developer.apple.com for QOS_CLASS_USER_INTERACTIVE doesn't find much. It seems that dispatch queues have priorities, but in this case I have a thread, not a dispatch queue. Any ideas?

Below is some simple code that does nothing, saves nothing. Yet the memory usage keeps rising. Am I missing something or is this a bug? The code requires 6 core CPU minimum. ContentView.swift import SwiftUI import Combine struct ContentView: View { @EnvironmentObject var loopClass:LoopClass var body: some View { ProgressView(value: Float(loopClass.loop_count), total: Float(loopClass.max_loops) ).progressViewStyle(.circular).padding() Button("Run looper", action: { loopClass.loopFunc() } ) } } LoopClass.swift import Combine class LoopClass: ObservableObject { @Published var loop_count = 0 @Published var max_loops = 0 func loopFunc () { let loopSet = [ 1, 3, 5, 7, 11, 13 ] max_loops = Int(pow(Double(loopSet.count), 13.0)) print("max_loops = \(max_loops)") for loop13 in loopSet { DispatchQueue.global().async { for loop12 in loopSet { for loop11 in loopSet { for loop10 in loopSet { for loop9 in loopSet { for loop8 in loopSet { for loop17 in loopSet { for loop16 in loopSet { for loop5 in loopSet { for loop4 in loopSet { for loop3 in loopSet { for loop2 in loopSet { for loop1 in loopSet { DispatchQueue.main.async{ self.loop_count += 1 } } }}}}}}}}}}} } // DQ } // for loop13 } }

Do run loops use an operation queue under the hood? When I dispatch to the mian queue, I know it will run on the mian thread, which means it will be handled b the main thread's run loop. But is the other way around correct? More specific question, is it possible somehow that the following code will return true? OperationQueue.current != OperationQueue.main && Thread.isMainThread I tried to do for example to dispatch to the main thread using a timer. myQueue.sync { let timer = Timer(timeInterval: 1, repeats: false) { _ in let curr = OperationQueue.current let main = OperationQueue.main print("\(String(describing: curr)) \(main)") } RunLoop.main.add(timer, forMode: .common) } And got the same pointer. But maybe some other way of dispatching to the main run loop will give different results, possibly that is why OperationQueue.current can return nil.

I'm running a simulation (SwiftUI app), which has 100 steps. I need each step to be executed in order. A first try was to dispatch with delay to schedule each second: for step in 0..<100 { DispatchQueue.main.asyncAfter(deadline: .now() + Double(step) * 1.0) { // simulation code } } Very poor results as 100 running threads are too much load for the system. So I split in 2 stages: for bigStep in 0..<10 { DispatchQueue.main.asyncAfter(deadline: .now() + Double(bigStep) * 10.0 ) { for step in 0..<10 { DispatchQueue.main.asyncAfter(deadline: .now() + Double(step) * 1.0) { // simulation code } } } } It works much better, as now there are a max of 20 threads active (in fact I create more levels to limit to a max of 8 concurrent threads). It addition, it allows to interrupt the simulation before end. My questions: is it the appropriate pattern ? Would a timer be better ? Other options ?