webapi 异步返回

 [HttpGet]
        public ApiActionResult OnceBackDemo()
        {
            var result = new ApiActionResult()
            {
                Success = false,
                Result = null,
                Message = "操作失败。"
            };
            System.Threading.ManualResetEvent mre = new System.Threading.ManualResetEvent(false);
            mre.Reset();
            Random rm = new Random();
            Action<Stopwatch> task = (sw) =>
            {
                sw.Start();
                int rm_val = rm.Next(1000);
                System.Threading.Thread.Sleep(rm_val);
            };
            var sw_out = new Stopwatch();
            task.BeginInvoke(sw_out, (ar) =>
            {
                task.EndInvoke(ar);
                mre.Set();
                sw_out.Stop();
                result.Success = true;
                result.Message = DateTime.Now + "->操作成功,耗时：" + sw_out.ElapsedMilliseconds.ToString()+"毫秒。";
            }, null);
            if (!mre.WaitOne(1500))
            {
                return result; 
            }
            return result;
        }