正由另一进程使用，因此该进程无法访问该文件

/// <summary>
        /// 写入日志
        /// </summary>
        /// <param name="log"></param>
        private void WriteLog(string log)
        {
            //edit at 2012.10.17 改成无锁异步写如日志文件
            using (FileStream fs = new FileStream(DataLogFile, FileMode.Append, FileAccess.Write, FileShare.Write, 1024, FileOptions.Asynchronous))
            {
                byte[] buffer = System.Text.Encoding.UTF8.GetBytes(log+"\r\n");
                IAsyncResult writeResult = fs.BeginWrite(buffer, 0, buffer.Length,
                    (asyncResult) =>
                    {
                        FileStream fStream = (FileStream)asyncResult.AsyncState;
                        fStream.EndWrite(asyncResult);
                    },
                    fs);
                //fs.EndWrite(writeResult);//这种方法异步起不到效果
                fs.Close();
            }
 
            //lock (lockObj)
            //{
 
            //    //using (StreamWriter sw = File.AppendText(DataLogFile))
            //    //{
 
            //    //    sw.WriteLine(log);
            //    //    sw.Flush();
            //    //    sw.Close();
            //    //}
            //}
        }class Program

{

    static void Main(string[] args)

    {

        ThreadPool.QueueUserWorkItem(run);

        ThreadPool.QueueUserWorkItem(run);

        Console.ReadLine();

    }

    private static void run(object state)

    {

        while (true)

        {

            Append();

        }

    }

    public static void Append()

    {

        try

        {

            //lock (typeof(Program))

            //{

                using (var writer = File.AppendText("1.txt"))

                {

                    writer.Write(DateTime.Now.ToString("HHmmss"));

                }

                Console.WriteLine("Done");

            //}

        }

        catch (Exception ex)

        {

            Console.WriteLine(ex);

        }           

    }

}
        static System.Threading.Semaphore _mutex = new System.Threading.Semaphore(1, 1, "IOHelper.Save");
        private static bool Save(string fileName, string text, bool isAppend)
        {
            try
            {
                if (_mutex.WaitOne(2000, false))//进程间同步。
                {
                    using (StreamWriter writer = new StreamWriter(fileName, isAppend))
                    {
                        writer.Write(text);
                    }
                }
                return true;
            }
            catch (Exception err)
            {
                Log.WriteLogToTxt(err);
            }
            finally
            {
                try
                {
                    _mutex.Release();
                }
                catch
                {

                }
            }
            return false;
        }

 

 

http://www.cnblogs.com/cyq1162/archive/2013/03/29/2988035.html