异步读写数据流

一、异步读取数据

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Threading;
 
namespace UseBeginRead
{
    class Program
    {
        //定义异步读取状态类
        class AsyncState
        {
            public FileStream FS { get; set; }
 
            public byte[] Buffer { get; set; }
 
            public ManualResetEvent EvtHandle { get; set; }
        }
 
        static  int bufferSize = 512;
 
        static void Main(string[] args)
        {
            string filePath = "d:\\test.txt";
            //以只读方式打开文件流
            using (var fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
            {
                var buffer = new byte[bufferSize];
 
                //构造BeginRead需要传递的状态
                var asyncState = new AsyncState { FS = fileStream, Buffer = buffer ,EvtHandle = new ManualResetEvent(false)};
 
                //异步读取
                IAsyncResult asyncResult = fileStream.BeginRead(buffer, 0, bufferSize, new AsyncCallback(AsyncReadCallback), asyncState);
 
                //阻塞当前线程直到读取完毕发出信号
                asyncState.EvtHandle.WaitOne();
                Console.WriteLine();
                Console.WriteLine("read complete");
                Console.Read();
            }
        }
 
        //异步读取回调处理方法
        public static void AsyncReadCallback(IAsyncResult asyncResult)
        {
            var asyncState = (AsyncState)asyncResult.AsyncState;
            int readCn = asyncState.FS.EndRead(asyncResult);
            //判断是否读到内容
            if (readCn > 0)
            {
                byte[] buffer;
                if (readCn == bufferSize) buffer = asyncState.Buffer;
                else
                {
                    buffer = new byte[readCn];
                    Array.Copy(asyncState.Buffer, 0, buffer, 0, readCn);
                }
 
                //输出读取内容值
                string readContent = Encoding.UTF8.GetString(buffer);
                 
                Console.Write(readContent);
            }
 
            if (readCn < bufferSize)
            {
                asyncState.EvtHandle.Set();
            }
            else {
                Array.Clear(asyncState.Buffer, 0, bufferSize);
                //再次执行异步读取操作
                asyncState.FS.BeginRead(asyncState.Buffer, 0, bufferSize, new AsyncCallback(AsyncReadCallback), asyncState);
            }
        }
    }
}

 二、异步写入数据

class Program
    {
        /// <summary>
        /// 异步回调需要的参数封装类
        /// </summary>
        class AsyncState {
            public int WriteCountOnce { get; set; }
 
            public int Offset { get; set; }
 
            public byte[] Buffer { get; set; }
 
            public ManualResetEvent WaitHandle { get; set; }
 
            public FileStream FS { get; set; }
        }
 
        static void Main(string[] args)
        {
            //准备一个1K的字节数组
            byte[] toWriteBytes = new byte[1 << 10];
            for (int i = 0; i < toWriteBytes.Length; i++)
            {
                toWriteBytes[i] = (byte)(i % byte.MaxValue);
            }
 
            string filePath = "d:\\test.txt";
            //FileStream实例
            using (var fileStream = new FileStream(filePath, FileMode.Create, FileAccess.ReadWrite, FileShare.Read))
            { 
                int offset = 0;
                //每次写入32字节
                int writeCountOnce = 1 << 5;
 
                //构造回调函数需要的状态
                AsyncState state = new AsyncState{
                    WriteCountOnce = writeCountOnce,
                    Offset = offset,
                    Buffer = toWriteBytes,
                    WaitHandle = new ManualResetEvent(false),
                    FS = fileStream
                };
 
                //做异步写操作
                fileStream.BeginWrite(toWriteBytes, offset, writeCountOnce, WriteCallback, state);
 
                //等待写完毕或者出错发出的继续信号
                state.WaitHandle.WaitOne();
            }
 
            Console.WriteLine("Done");
 
            Console.Read();
        }
 
        /// <summary>
        /// 异步写的回调函数
        /// </summary>
        /// <param name="asyncResult">写状态</param>
        static void WriteCallback(IAsyncResult asyncResult)
        {
            AsyncState state = (AsyncState)asyncResult.AsyncState;
             
            try
            {
                state.FS.EndWrite(asyncResult);
            }
            catch (Exception ex)
            {
                Console.WriteLine("EndWrite Error:" + ex.Message);
                state.WaitHandle.Set();
                return;
            }
 
            Console.WriteLine("write to " + state.FS.Position);
            //判断是否写完，未写完继续异步写
            if (state.Offset + state.WriteCountOnce < state.Buffer.Length)
            {
                state.Offset += state.WriteCountOnce;
                Console.WriteLine("call BeginWrite again");
                state.FS.BeginWrite(state.Buffer, state.Offset, state.WriteCountOnce, WriteCallback, state);
            }
            else {
                //写完发出完成信号
                state.WaitHandle.Set();
            }
        }