public class Service:IContracts
    {
        private const string baseLocation = @"E:\";
        private FileStream _stream;
        private byte[] _buffer;
        public double Add(double x, double y)
        {
            return x + y;
        }
 
        public IAsyncResult BeginAsy(string fileName, AsyncCallback userCallback, object stateObject)
        {
             this._stream = new FileStream(baseLocation + fileName, FileMode.Open, FileAccess.Read, FileShare.Read);
             this._buffer = new byte[this._stream.Length];
             return this._stream.BeginRead(this._buffer, 0, this._buffer.Length, userCallback, stateObject);
        }

        public string EndAsy(IAsyncResult ar)
        {
            this._stream.EndRead(ar);
            this._stream.Close();
            Thread.Sleep(3000);
            return Encoding.ASCII.GetString(this._buffer);
         }


    }

proxy.BeginAsy("test.txt", asy =>   //test.txt是大文件 【1】
            {
                Console.WriteLine(proxy.EndAsy(asy));
            }, null);
 Console.WriteLine(proxy.Add(1.0, 1.0));【2】