Measure iOS app startup time, in seconds, from the time user tapped an icon on the home screen (using time, when app process was created). Swift 4.

MeasureAppStartupTime.swift

// Returns number of seconds passed between time when process was created and function was called
func measureAppStartUpTime() -> Double {
    var kinfo = kinfo_proc()
    var size = MemoryLayout<kinfo_proc>.stride
    var mib : [Int32] = [CTL_KERN, KERN_PROC, KERN_PROC_PID, getpid()]
    sysctl(&mib, u_int(mib.count), &kinfo, &size, nil, 0)
    let start_time = kinfo.kp_proc.p_starttime
    var time : timeval = timeval(tv_sec: 0, tv_usec: 0)
    gettimeofday(&time, nil)
    let currentTimeMilliseconds = Double(Int64(time.tv_sec) * 1000) + Double(time.tv_usec) / 1000.0
    let processTimeMilliseconds = Double(Int64(start_time.tv_sec) * 1000) + Double(start_time.tv_usec) / 1000.0
    return (currentTimeMilliseconds - processTimeMilliseconds) / 1000.0
}