源码
https://gitee.com/s0611163/AsyncAwaitDemo
为什么会研究这个？
我们项目的客户端和服务端通信用的是WCF，我就想，能不能用异步的方式调用WCF服务呢？或者说能不能用async await的方式调用WCF服务呢？
然后我发现WCF是通过BeginXXX和EndXXX这种回调的方式实现异步的，似乎不支持async await语法糖，那只能通过状态机的方式实现了，不然多个请求就会写成回调地狱。
如果用Task.Run包起来，里面再写个Wait，这就是假异步，还不如不用异步，按原来非异步的方式写。
研究了回调和状态机之后，又看了相关的博客，就像一篇博客里说的，调用WCF不难，异步调用WCF不难，异步调用WCF并保证调用顺序也不难，难的是实现了这些之后，代码的可读性和可维护性。
所以我的结论是，调用WCF，如果没有特殊需求，还是不要异步的好，写起来复杂。
C# 同步 异步 回调 状态机 async await Demo
主要演示了不使用async、await语法糖，通过回调函数和状态机实现异步
为什么要写这个Demo？
为了帮助理解异步，async、await经过编译生成的状态机代码，有点复杂，这个Demo里写了一个相对简单的状态机代码，便于理解
代码说明
代码中主要写了三种下载文件的示例
- 同步方式下载文件，为了防止下载较大文件时卡住界面，代码在线程中执行，文件下载完成之前，始终占用一个线程
- 异步方式下载文件，使用了async、await语法糖，下载文件时，可以看到，workerThreads(可用线程数)和completionPortThreads(可用异步线程数)会发生变化，但是不会长时间占用一个线程
- 异步方式下载文件，不使用async、await语法糖，通过回调函数和状态机实现，workerThreads(可用线程数)和completionPortThreads(可用异步线程数)会发生变化，但是不会长时间占用一个线程
结论：异步的本质是回调，异步是回调的语法糖
- 相比同步方式，使用异步方式下载文件时，忽略掉误差，下载速度并没有更快，异步的主要优点是不会长时间占用一个线程
- 在没有async、await语法糖时，使用回调函数和状态机也可以实现异步，但代码写的不够优雅，心智负担重，所以async、await的另一个优点是使代码简单
- 异步的本质就是回调，C#异步底层是通过系统级回调和状态机实现的，async、await会被编译成状态机代码，相关于用代码生成器生成了代码，但这个代码自己写的话，心智负担重
- 不使用async、await语法糖的前提下，使用状态机可以避免回调地狱
- 即使不使用async、await语法糖，依然感受到了异步的侵入性，没办法在底层完全封装起来，代码一直侵入到控件的事件里，使用async、await也是，你从代码的底层，写async一直写到控件的事件层
思考：
经测试，button4_Click、button5_Click、button6_Click在下载大文件时，耗时较长，但是界面并不会卡住，依然可以*拖动窗体或点击其它按钮
button4_Click、button5_Click、button6_Click方法分别调用了AsyncFunctionWithCallback方法
AsyncFunctionWithCallback方法调用了HttpUtil类的HttpDownloadFileAsyncWithCallback方法
请仔细观察上面的方法，它们没有使用new Thread、Task.Run、Task.Factory.StartNew等线程相关的方法，
也就是说执行长时间操作，没有阻塞界面，但是又没有使用线程，
实际上下载文件过程中，没有使用C#的CLR线程池，测试时，workerThreads数量不会变化，但是你会看到completionPortThreads数量变化，
下载文件的过程使用了异步线程池，但是下载大文件时，并不会长时间占用异步线程池
Demo截图
测试代码Form1.cs
using Models;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
using Utils;
namespace AsyncAwaitDemo
{
public partial class Form1 : Form
{
private DateTime _dt1;
private System.Timers.Timer _timer;
private string _testFileDownloadUrl = "http://desk-fd.zol-img.com.cn/t_s1920x1080c5/g6/M00/06/00/ChMkKWHXqV-IJFpUAEJatCdq_LUAAXW8AA1PvwAQlrM029.jpg?downfile=1642227460763.jpg"; //文件下载测试URL
//private string _testFileDownloadUrl = "https://down21.xiazaidb.com/app/xiaomanghe.apk"; //文件下载测试URL
//private string _testFileDownloadUrl = "https://codeload.github.com/0611163/DBHelper/zip/refs/heads/master"; //文件下载测试URL
//private string _testFileDownloadUrl = "http://down-ww5.537a.com/soft/3/ce/com.yhong.muchun_51982ada.apk"; //文件下载测试URL
//private string _testFileDownloadUrl = "https://dl.360safe.com/netunion/20140425/360se+191727+n3f07b78190.exe"; //文件下载测试URL 大一点的文件
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
//定时器会使用线程池中的一个线程
_timer = new System.Timers.Timer();
_timer.Interval = 100;
_timer.Elapsed += _timer_Elapsed;
_timer.Start();
}
#region Log
private void Log(string log)
{
if (!this.IsDisposed)
{
string msg = DateTime.Now.ToString("mm:ss.fff") + " " + log + "\r\n\r\n";
if (this.InvokeRequired)
{
this.BeginInvoke(new Action(() =>
{
textBox1.AppendText(msg);
}));
}
else
{
textBox1.AppendText(msg);
}
}
}
#endregion
#region _timer_Elapsed
private void _timer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
int workerThreads;
int completionPortThreads;
int maxWorkerThreads;
int maxCompletionPortThreads;
ThreadPool.GetAvailableThreads(out workerThreads, out completionPortThreads);
ThreadPool.GetMaxThreads(out maxWorkerThreads, out maxCompletionPortThreads);
this.BeginInvoke(new Action(() =>
{
label1.Text = "程序当前使用线程数：" + (maxWorkerThreads - workerThreads) + " workerThreads：" + workerThreads.ToString() + " completionPortThreads：" + completionPortThreads;
}));
}
#endregion
#region button1_Click 测试同步方法
private void button1_Click(object sender, EventArgs e)
{
Task.Run(() => //下载文件是耗时操作，需要在线程中执行，否则界面卡住
{
Log("开始");
DateTime dt = DateTime.Now;
//输入参数
string arg1 = "1";
string arg2 = "2";
string arg3 = "3";
//方法调用
string result1 = SyncFunction(arg1);
string result2 = SyncFunction(arg2);
string result3 = SyncFunction(arg3);
//输出结果
Log(result1);
Log(result2);
Log(result3);
Log("结束，耗时：" + DateTime.Now.Subtract(dt).TotalSeconds.ToString("0.000"));
});
}
#endregion
#region button2_Click 测试异步方法(三个异步方法并行，按顺序输出)
private async void button2_Click(object sender, EventArgs e)
{
Log("开始");
DateTime dt = DateTime.Now;
//输入参数
string arg1 = "1";
string arg2 = "2";
string arg3 = "3";
//方法调用
var t1 = AsyncFunction(arg1);
var t2 = AsyncFunction(arg2);
var t3 = AsyncFunction(arg3);
string result1 = await t1;
string result2 = await t2;
string result3 = await t3;
//输出结果
Log(result1);
Log(result2);
Log(result3);
Log("结束，耗时：" + DateTime.Now.Subtract(dt).TotalSeconds.ToString("0.000"));
}
#endregion
#region button3_Click 测试异步方法(三个异步方法顺序执行，按顺序输出)
private async void button3_Click(object sender, EventArgs e)
{
Log("开始");
DateTime dt = DateTime.Now;
//输入参数
string arg1 = "1";
string arg2 = "2";
string arg3 = "3";
//方法调用
string result1 = await AsyncFunction(arg1);
string result2 = await AsyncFunction(arg2);
string result3 = await AsyncFunction(arg3);
//输出结果
Log(result1);
Log(result2);
Log(result3);
Log("结束，耗时：" + DateTime.Now.Subtract(dt).TotalSeconds.ToString("0.000"));
}
#endregion
#region button4_Click 测试状态机(三个异步方法顺序执行，按顺序输出)(等价于button3_Click)
private void button4_Click(object sender, EventArgs e)
{
List<object> resultList = new List<object>();
//回调、状态机，不使用async await语法糖
Action<int, object> awaitAction = null;
awaitAction = (state, result) =>
{
//输入参数
string arg1 = "1";
string arg2 = "2";
string arg3 = "3";
//方法调用
if (state == 0)
{
Log("开始");
_dt1 = DateTime.Now;
AsyncFunctionWithCallback(arg1, r => awaitAction(1, r));
return;
}
if (state == 1)
{
resultList.Add(result);
AsyncFunctionWithCallback(arg2, r => awaitAction(2, r));
return;
}
if (state == 2)
{
resultList.Add(result);
AsyncFunctionWithCallback(arg3, r => awaitAction(3, r));
return;
}
//输出结果
if (state == 3)
{
resultList.Add(result);
foreach (object item in resultList)
{
Log(item != null ? item.ToString() : "null");
}
Log("结束，耗时：" + DateTime.Now.Subtract(_dt1).TotalSeconds.ToString("0.000"));
return;
}
};
awaitAction(0, null);
}
#endregion
#region button5_Click 测试状态机(三个异步方法并行，按顺序输出)(等价于button2_Click)
private void button5_Click(object sender, EventArgs e)
{
object[] resultArray = new object[3];
//是否已调用回调函数
bool _completedCalled = false;
//锁
object _lock = new object();
//输出结果
Action<object[]> output = arr =>
{
if (arr.Count(a => a != null) == 3)
{
lock (_lock)
{
if (!_completedCalled)
{
_completedCalled = true;
foreach (object item in arr)
{
Log(item != null ? item.ToString() : "null");
}
Log("结束，耗时：" + DateTime.Now.Subtract(_dt1).TotalSeconds.ToString("0.000"));
}
}
}
};
//回调、状态机，不使用async await语法糖
Action<int, object> awaitAction = null;
awaitAction = (state, result) =>
{
//输入参数
string arg1 = "1";
string arg2 = "2";
string arg3 = "3";
//方法调用
if (state == 0)
{
Log("开始");
_dt1 = DateTime.Now;
AsyncFunctionWithCallback(arg1, r => awaitAction(1, r));
AsyncFunctionWithCallback(arg2, r => awaitAction(2, r));
AsyncFunctionWithCallback(arg3, r => awaitAction(3, r));
return;
}
//输出结果
if (state == 1)
{
resultArray[0] = result;
output(resultArray);
return;
}
if (state == 2)
{
resultArray[1] = result;
output(resultArray);
return;
}
if (state == 3)
{
resultArray[2] = result;
output(resultArray);
return;
}
};
awaitAction(0, null);
}
#endregion
#region button6_Click 测试状态机(三个异步方法并行，按顺序输出)(等价于button2_Click)(相对于button5_Click更优雅的实现)
private void button6_Click(object sender, EventArgs e)
{
Log("开始");
DateTime dt = DateTime.Now;
//输入参数
string arg1 = "1";
string arg2 = "2";
string arg3 = "3";
//操作结果
object result1 = null;
object result2 = null;
object result3 = null;
//方法调用
Await await = new Await();
await.Add(() => AsyncFunctionWithCallback(arg1, r => await.Collect(r, out result1)))
.Add(() => AsyncFunctionWithCallback(arg2, r => await.Collect(r, out result2)))
.Add(() => AsyncFunctionWithCallback(arg3, r => await.Collect(r, out result3)))
.Completed(resultList => //输出结果
{
Log(result1 != null ? result1.ToString() : "null");
Log(result2 != null ? result2.ToString() : "null");
Log(result3 != null ? result3.ToString() : "null");
Log("结束，耗时：" + DateTime.Now.Subtract(dt).TotalSeconds.ToString("0.000"));
})
.Start();
}
#endregion
#region button7_Click 不使用状态机，执行带回调的异步方法(基本等价于button1_Click)
private void button7_Click(object sender, EventArgs e)
{
Task.Run(() =>
{
Log("开始");
DateTime dt = DateTime.Now;
//输入参数
string arg1 = "1";
string arg2 = "2";
string arg3 = "3";
//操作结果
object result1 = null;
object result2 = null;
object result3 = null;
//方法调用
AsyncFunctionWithCallback(arg1, r => result1 = r);
AsyncFunctionWithCallback(arg2, r => result2 = r);
AsyncFunctionWithCallback(arg3, r => result3 = r);
//等待三个操作结果全部返回，三个操作结果返回之前，始终占用一个线程
while (result1 == null || result2 == null || result3 == null)
{
Thread.Sleep(1);
}
//输出结果
Log(result1 != null ? result1.ToString() : "null");
Log(result2 != null ? result2.ToString() : "null");
Log(result3 != null ? result3.ToString() : "null");
Log("结束，耗时：" + DateTime.Now.Subtract(dt).TotalSeconds.ToString("0.000"));
});
}
#endregion
#region 同步方法
/// <summary>
/// 同步方法
/// </summary>
private string SyncFunction(string arg)
{
MemoryStream ms = HttpUtil.HttpDownloadFile(_testFileDownloadUrl);
return "同步方法 arg=" + arg + " 下载文件的字节数组长度=" + ms.Length;
}
#endregion
#region 异步方法
/// <summary>
/// 异步方法
/// </summary>
private async Task<string> AsyncFunction(string arg)
{
MemoryStream ms = await HttpUtil.HttpDownloadFileAsync(_testFileDownloadUrl);
return "异步方法 arg=" + arg + " 下载文件的字节数组长度=" + ms.Length;
}
#endregion
#region 带回调的异步方法
/// <summary>
/// 带回调的异步方法
/// </summary>
/// <param name="arg">传入参数</param>
/// <param name="callback">回调</param>
/// <param name="nextState">下一个状态</param>
private void AsyncFunctionWithCallback(string arg, Action<object> callback)
{
HttpUtil.HttpDownloadFileAsyncWithCallback(_testFileDownloadUrl, new HttpUtilAsyncState() { State = 0 }, obj =>
{
if (obj is Exception)
{
Exception ex = obj as Exception;
Log("错误：" + ex.Message);
}
else
{
MemoryStream ms = obj as MemoryStream;
string result = "带回调的异步方法 arg=" + arg + " 下载文件的字节数组长度=" + ms.Length;
callback(result);
}
});
}
#endregion
#region 用Task模拟的异步方法
/*
#region 异步方法
/// <summary>
/// 异步方法
/// </summary>
private Task<string> AsyncFunction(string arg)
{
return Task.Run<string>(() =>
{
Thread.Sleep(2000);
return "异步方法 arg=" + arg;
});
}
#endregion
#region 带回调的异步方法
/// <summary>
/// 带回调的异步方法
/// </summary>
/// <param name="arg">传入参数</param>
/// <param name="callback">回调</param>
/// <param name="nextState">下一个状态</param>
private void AsyncFunctionWithCallback(string arg, Action<object> callback)
{
Task.Run(() =>
{
if (arg == "1")
{
Thread.Sleep(2000);
}
else
{
Thread.Sleep(2000);
}
string result = "带回调的异步方法 arg=" + arg;
callback(result);
});
}
#endregion
*/
#endregion
}
}
异步工具类Await.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Utils
{
/// <summary>
/// 异步工具类
/// 代替async await语法糖
/// </summary>
public class Await
{
/// <summary>
/// 状态
/// </summary>
private int _state { get; set; }
/// <summary>
/// 异步操作集合
/// </summary>
private List<Action> _actionList = new List<Action>();
/// <summary>
/// 操作结果集合
/// </summary>
private List<object> _resultList = new List<object>();
/// <summary>
/// 完成后的回调
/// </summary>
private Action<List<object>> _completedCallback;
/// <summary>
/// 是否已调用回调函数
/// </summary>
private bool _completedCalled = false;
/// <summary>
/// 锁
/// </summary>
private object _lock = new object();
/// <summary>
/// 异步工具类 构造函数
/// </summary>
public Await()
{
_state = 0;
}
/// <summary>
/// 添加一个异步操作
/// </summary>
public Await Add(Action action)
{
_actionList.Add(action);
return this;
}
/// <summary>
/// 开始执行
/// </summary>
public Await Start()
{
foreach (Action action in _actionList)
{
action();
}
return this;
}
/// <summary>
/// 收集结果
/// </summary>
public Await Collect(object result, out object outResult)
{
outResult = result;
_resultList.Add(result);
lock (_lock)
{
_state++;
if (_state == _actionList.Count && _completedCallback != null && !_completedCalled)
{
_completedCalled = true;
_completedCallback(_resultList);
}
}
return this;
}
/// <summary>
/// 注册完成后的回调函数
/// </summary>
public Await Completed(Action<List<object>> completedCallback)
{
this._completedCallback = completedCallback;
return this;
}
}
}
文件下载工具类HttpUtil.cs
下面的代码使用了三种方式实现文件下载
- 同步方式实现文件下载
- 异步方式实现文件下载
- 通过回调和状态机实现的异步下载
using Models;
using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace Utils
{
/// <summary>
/// Http上传下载文件
/// </summary>
public class HttpUtil
{
#region HttpDownloadFile 下载文件
/// <summary>
/// 下载文件
/// </summary>
/// <param name="url">下载文件url路径</param>
/// <param name="cookie">cookie</param>
public static MemoryStream HttpDownloadFile(string url, CookieContainer cookie = null, WebHeaderCollection headers = null)
{
try
{
// 设置参数
HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
request.Method = "GET";
request.CookieContainer = cookie;
if (headers != null)
{
foreach (string key in headers.Keys)
{
request.Headers.Add(key, headers[key]);
}
}
//发送请求并获取相应回应数据
HttpWebResponse response = request.GetResponse() as HttpWebResponse;
//直到request.GetResponse()程序才开始向目标网页发送Post请求
Stream responseStream = response.GetResponseStream();
//创建写入流
MemoryStream stream = new MemoryStream();
byte[] bArr = new byte[10240];
int size = responseStream.Read(bArr, 0, (int)bArr.Length);
while (size > 0)
{
stream.Write(bArr, 0, size);
size = responseStream.Read(bArr, 0, (int)bArr.Length);
}
stream.Seek(0, SeekOrigin.Begin);
responseStream.Close();
return stream;
}
catch (Exception ex)
{
throw ex;
}
}
#endregion
#region HttpDownloadFile 下载文件(异步)
/// <summary>
/// 下载文件
/// </summary>
/// <param name="url">下载文件url路径</param>
/// <param name="cookie">cookie</param>
public static async Task<MemoryStream> HttpDownloadFileAsync(string url, CookieContainer cookie = null, WebHeaderCollection headers = null)
{
try
{
// 设置参数
HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
request.Method = "GET";
request.CookieContainer = cookie;
if (headers != null)
{
foreach (string key in headers.Keys)
{
request.Headers.Add(key, headers[key]);
}
}
//发送请求并获取相应回应数据
HttpWebResponse response = await request.GetResponseAsync() as HttpWebResponse;
//直到request.GetResponse()程序才开始向目标网页发送Post请求
Stream responseStream = response.GetResponseStream();
//创建写入流
MemoryStream stream = new MemoryStream();
byte[] bArr = new byte[10240];
int size = await responseStream.ReadAsync(bArr, 0, (int)bArr.Length);
while (size > 0)
{
stream.Write(bArr, 0, size);
size = await responseStream.ReadAsync(bArr, 0, (int)bArr.Length);
}
stream.Seek(0, SeekOrigin.Begin);
responseStream.Close();
return stream;
}
catch (Exception ex)
{
throw ex;
}
}
#endregion
#region HttpDownloadFile 下载文件(基于回调的异步)
/// <summary>
/// 下载文件
/// </summary>
/// <param name="url">下载文件url路径</param>
/// <param name="cookie">cookie</param>
public static void HttpDownloadFileAsyncWithCallback(string url, HttpUtilAsyncState state = null, Action<object> callback = null, CookieContainer cookie = null, WebHeaderCollection headers = null)
{
try
{
if (state.State == 0)
{
// 设置参数
HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
request.Method = "GET";
request.CookieContainer = cookie;
if (headers != null)
{
foreach (string key in headers.Keys)
{
request.Headers.Add(key, headers[key]);
}
}
//发送请求并获取相应回应数据
request.BeginGetResponse(asyncResult =>
{
HttpUtilAsyncState asyncState = asyncResult.AsyncState as HttpUtilAsyncState;
try
{
HttpWebResponse response = request.EndGetResponse(asyncResult) as HttpWebResponse;
asyncState.ResponseStream = response.GetResponseStream();
HttpDownloadFileAsyncWithCallback(null, asyncState, callback);
}
catch (Exception ex)
{
asyncState.Exception = ex;
asyncState.State = 2;
HttpDownloadFileAsyncWithCallback(null, asyncState, callback);
}
}, new HttpUtilAsyncState { Request = request, State = 1 });
return;
}
if (state.State == 1)
{
byte[] bArr = new byte[10240];
state.ResponseStream.BeginRead(bArr, 0, (int)bArr.Length, asyncResult =>
{
HttpUtilAsyncState asyncState = asyncResult.AsyncState as HttpUtilAsyncState;
try
{
int size = state.ResponseStream.EndRead(asyncResult);
if (size > 0)
{
state.Stream.Write(bArr, 0, size);
HttpDownloadFileAsyncWithCallback(null, asyncState, callback);
}
else
{
asyncState.State = 2;
HttpDownloadFileAsyncWithCallback(null, asyncState, callback);
}
}
catch (Exception ex)
{
asyncState.Exception = ex;
asyncState.State = 2;
HttpDownloadFileAsyncWithCallback(null, asyncState, callback);
}
}, state);
return;
}
if (state.State == 2)
{
if (state.Exception != null)
{
callback(state.Exception);
return;
}
else
{
state.Stream.Seek(0, SeekOrigin.Begin);
state.ResponseStream.Close();
callback(state.Stream);
return;
}
}
}
catch (Exception ex)
{
throw ex;
}
}
#endregion
}
}