GCD 多线程

Concurrent Queue

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

Serial Queue

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

Main Queue

DispatchQueue.main.async{
}

DispatchQueue.main.sync {
}

Background Queue

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

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