Run Multiple Parallel Process And Wait For Completion-Child App

class Program
{
    private static T Deserialize(string objStr)
    {
        byte[] b = Convert.FromBase64String(objStr);
        using (var stream = new MemoryStream(b))
        {
            var formatter = new BinaryFormatter();
            stream.Seek(0, SeekOrigin.Begin);
            return (T)formatter.Deserialize(stream);
        }
    }
    static void Main(string[] args)
    {

        string strArg = args[0];
        var arg = Deserialize(strArg);
        for (int i = 0; i <= arg.UrlList.Count; i++)
        {
            var uri = new Uri(arg.UrlList[i]);
            var localFileName = System.IO.Path.GetFileName(uri.LocalPath);
            try
            {
                WebClient webClient = new WebClient();
                webClient.DownloadFile(uri, localFileName);

                Console.WriteLine(localFileName + "...ok");
            }
            catch (Exception ex)
            {
                Console.WriteLine(localFileName + "...err" + ex.Message);
            }

        }

    }
}