dispatch_after Swift3

dispatch_after.swift

import UIKit

var str = "Hello, playground"
let x = UINT32_MAX

print(Date())
let q = DispatchQueue.init(label: "test", qos: .background, attributes: .init(rawValue: 0), autoreleaseFrequency: .never, target: nil)
var flag = true
print(q.label)
q.asyncAfter(deadline: .now() + 3) {
    if flag {
        print("\(Date()) 500 msec seconds later")
    }else {
        print("\(Date()) 500 cancel")
    }
    
}

for i in 0 ..< 100 {
    print(Date())
    sleep(1)
    flag = false
}