Tips for using DispatchQueue

Tips

• UI operations should only happen in main queue. DispatchQueue.main.async {}
• API calls: DispatchQueue(label: "api-queue").async {}
• Check current queue: print("\(#function) is running at \(Thread.current)")
• Check is on main thread: Thread.current.isMainThread
• DispatchQueue.main.sync{} will cause crash
• Delay DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {}

• Tasks in DispatchQueue.main.async from main thread will still be executed in main thread after all the other execution finished. For example:

The output will be:

Different Quality of Service in Apple's documentation

     DispatchQueue(label: "userInteractive", qos: .userInteractive)