testGCD_4.swift

       // 非同步佇列的使用方式與驗證非同步執行的結果
        let concurrentQueue1: DispatchQueue = DispatchQueue(label: "concurrentQueue1", attributes: .concurrent)
        
        let concurrentQueue2: DispatchQueue = DispatchQueue(label: "concurrentQueue2", attributes: .concurrent)
        
        let concurrentQueue3: DispatchQueue = DispatchQueue(label: "concurrentQueue3", attributes: .concurrent)
        
        concurrentQueue1.async {
            for i in 1 ... 10 {
                print("i: \(i)")
            }
        }
        
        concurrentQueue2.async {
            for j in 100 ... 109 {
                print("j: \(j)")
            }
        }
        
        concurrentQueue3.async {
            for k in 200 ... 209 {
                print("k: \(k)")
            }
        }