C# 文件异步操作

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

//文件异步操作
namespace FileAsynchronousOperation
{
    class Program
    {
        static void Main(string[] args)
        {
            //实例化MyFile类
            MyFile myFile = new MyFile();
            //定义参数
            string filePath = "D:\testasy.txt";
            string msg = "helloworld";
            //调用异步操作方法
            myFile.AsynchronousOperation(filePath,msg);
        }
    }
    /// <summary>
    /// 文件
    /// </summary>
    class MyFile
    {
        /// <summary>
        /// 文件异步操作
        /// </summary>
        /// <param name="filePath">文件路径</param>
        /// <param name="msg">写入内容</param>
        public void AsynchronousOperation(string filePath,string msg)
        {
            FileStream fileSteam = null;
            
            FileInfo fileinfo = new FileInfo(filePath);
            //判断文件是否存在
            if (!fileinfo.Exists)
            {
                fileSteam = fileinfo.Create();
                Console.WriteLine("创建文件{0}", filePath);
                fileSteam.Close();
            }
            fileSteam = new FileStream(filePath, FileMode.Open, FileAccess.Write, FileShare.None, 4096, true);
            Console.WriteLine("开启异步操作{0}", fileSteam.IsAsync);
            byte[] buffer = Encoding.Default.GetBytes(msg);
            //开始执行异步操作
            IAsyncResult asynncResult = fileSteam.BeginWrite(buffer,0, buffer.Length, new AsyncCallback(EndWriteCallBack), fileSteam);
            Console.WriteLine("开始异步写入请稍候...");
            Console.Read();
        }
        /// <summary>
        /// 回调函数
        /// </summary>
        /// <param name="asyncResult">状态</param>
        public void EndWriteCallBack(IAsyncResult asyncResult)
        {
            Console.WriteLine("异步写入开始...");
            FileStream stream = asyncResult.AsyncState as FileStream;//转化为FileStream类型
            if (stream!=null)
            {
                stream.EndWrite(asyncResult);
                stream.Close();
            }
            Console.WriteLine("写入完成");

        }
    }
}

Filestreom 在对文件进行异步操作时，对大数据量读写操作使用 BeginRead 和 Begin 树 rite 方法的效果更好；
而对于数据量较少的读写操作，使川异步方式的速度可能会比同步方式要慢。
所以，你需要针对应用程序的实际情况决定是否要选择异步处理方式。