Creating a concurrent queue in swift

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(qos: .background).async {

}
Xcode 8.2 beta 2:
To get one of the background thread
DispatchQueue.global(qos: .default).async {

}

DispatchQueue.global().async {
    // qos' default value is ´DispatchQoS.QoSClass.default`
}
DispatchQueue.global(qos: .background).async {
    // Background Thread
    DispatchQueue.main.async {
        // Run UI Updates or call completion block
    }
}
If you want to learn about using these queues .See this answer

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