Get pre-main time

get_pre_main_time.swift

/// Call this at main()
/// return: time in milliseconds
func getPreMainTime() -> Double {
        let currentTimeIntervalInMilliSecond = Date().timeIntervalSince1970 * 1000.0
        var procInfo = kinfo_proc()
        let pid = ProcessInfo.processInfo.processIdentifier
        var cmd: [Int32] = [CTL_KERN, KERN_PROC, KERN_PROC_PID, pid]
        var size = MemoryLayout.stride(ofValue: procInfo)
        // Retrieve information of current process
        if sysctl(&cmd, UInt32(cmd.count), &procInfo, &size, nil, 0) == 0 {
            // tv_sec -> timestamp in second; tv_usec -> rest fraction part in microsecond
            let tvSecInMilliseconds = Double(procInfo.kp_proc.p_un.__p_starttime.tv_sec) * 1000.0
            let tvUsecInMilliseconds = Double(procInfo.kp_proc.p_un.__p_starttime.tv_usec) / 1000.0
            let processCreationTime = tvSecInMilliseconds + tvUsecInMilliseconds
            var premainTime = currentTimeIntervalInMilliSecond - processCreationTime
            premainTime.round()
            return premainTime
        } else {
            print("Can't retrieve information of process", category: .perfLogger)
        }
    }