C# async await的使用

class Program
    {
        static void Main(string[] args)
        {
            string tid = Thread.CurrentThread.ManagedThreadId.ToString();
            Console.WriteLine("当前位置主函数，调用async异步之前，线程ID"+tid);
            Task<int> t = CalAsync();
            Console.WriteLine("当前位置主函数，调用async异步之后，线程ID" + tid);
            Console.Read();

        }
        public static async Task<int> CalAsync()
        {
            string tid = Thread.CurrentThread.ManagedThreadId.ToString();
            Console.WriteLine("当前位置async函数，await之前，线程ID"+tid);
            int result = await Task.Run(new Func<int>(Cal));
            tid = Thread.CurrentThread.ManagedThreadId.ToString();
            Console.WriteLine("当前位置async函数，await之后，线程ID" + tid);
            return result;
        }

        public static int Cal()
        {
            string tid = Thread.CurrentThread.ManagedThreadId.ToString();
            Console.WriteLine("当前位置耗时函数，线程ID"+tid);
            int sum = 0;
            for (int i = 0; i < 999; i++)
            {
                sum = sum + i;
            }
            Console.WriteLine("当前位置耗时函数完成，线程ID" + tid);
            return sum;
        }


    }