From http://stackoverflow.com/questions/37805885/how-to-create-dispatch-queue-in-swift-3

threading, dispatch queue, queueing

Creating a concurrent queue

let concurrentQueue = DispatchQueue(label: "queuename", attributes: .concurrent)
concurrentQueue.sync {

}  
Create a serial queue

let serialQueue = DispatchQueue(label: "queuename")
serialQueue.sync { 

}
Get main queue asynchronously

DispatchQueue.main.async {

}
Get main queue synchronously

DispatchQueue.main.sync {

}
To get one of the background thread

DispatchQueue.global(attributes: .qosDefault).async {

}
Xcode 8 beta 5:

To get one of the background thread

DispatchQueue.global(qos: DispatchQoS.QoSClass.default).async {

}

DispatchQueue.global().async {
    // qos' default value is ´DispatchQoS.QoSClass.default`
}