System Dispatch Queues

SystemDispatchQueues.swift

DispatchQueue.global(qos: .utility).async {
    // Asynchronous code running on the low priority queue
}

DispatchQueue.main.async {
    // Asynchronous code running on the main queue
}

DispatchQueue.global(qos: .userInitiated).sync {
    // Synchronous code running on the high prioriy queue
}