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

  1. 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
  2. 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
  3. 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

  1. 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
  2. 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
  3. 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
  4. 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
  5. 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,依然可以自由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

  1. 同步方式实现文件下载
  2. 异步方式实现文件下载
  3. 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 } }

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