C#中ManualResetEvent实现线程的暂停与恢复
时间：2022-05-16 08:45:51|栏目：.NET代码|点击： 次
背景
前些天遇到一个需求，在没有第三方源码的情况下，刷新一个第三方UI，并且拦截到其ajax请求的返回结果。当结果为AVALIABLE的时候，停止刷新并语音提示，否则继续刷新。
分析这个需求，发现需要控制一个刷新循环的暂停与开始，因此网上搜到了通过ManualResetEvent实现线程的暂停与恢复。
ManualResetEvent介绍
ManualResetEvent是一个通过信号机制，实现线程间状态同步的类。常用的方法有以下三个：
- WaitOne：阻止当前线程，直到收到信号
- Reset：将事件状态设置为非终止状态，导致线程阻止
- Set：将事件状态设置为终止状态，从而允许继续执行一个或多个等待线程
实现设计
1.通过CefSharp的谷歌浏览器插件请求第三方网站
2.具体交互逻辑如下
默认开启一个线程，并通过WaitOne挂起，等待手动开始自动刷新的指令
手动通过Set方法发送开始工作信号
执行完面操作后，通过Reset将线程再次挂起，并等待Ajax结果，判断Ajax结果，如果不等于AVALIABLE则再次恢复线程
public Form1()
{
InitializeComponent();
var setting = new CefSettings();
setting.Locale = "zh-CN";
setting.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 Safari/537.36";
// 避免页面加载不出来, 建议加上这句
Cef.Initialize(setting);
workerThread = new Thread(new ThreadStart(BeginListenWorkerAsync));
workerThread.IsBackground = true;
workerThread.Start();
this.停止自动监听ToolStripMenuItem.Enabled = false;
}
private async void BeginListenWorkerAsync()
{
while (true)
{
_eventBeginListenWorkList.WaitOne(); //1.默认挂起线程，等待信号
chromiumWebBrowser1.GetBrowser().MainFrame.ExecuteJavaScriptAsync(@"document.evaluate(""//*[@id='root']/div[1]/div[2]/div/div[2]/div[1]/div[1]/div/div[1]/button"", document).iterateNext().click()");
Thread.Sleep(1000);
chromiumWebBrowser1.GetBrowser().MainFrame.ExecuteJavaScriptAsync(@"document.evaluate(""//*[@id='root']/div[1]/div[2]/div/div[1]/div/div/div/div[2]/div[6]/div/button"", document).iterateNext().click()");
_eventBeginListenWorkList.Reset(); //3.页面执行完相应操作则再次挂起线程，等待ajax请求结果再判断是否恢复线程
}
}
private void 停止自动监听ToolStripMenuItem_Click(object sender, EventArgs e)
{
this.开始自动监听ToolStripMenuItem.Enabled = true;
this.停止自动监听ToolStripMenuItem.Enabled = false;
_eventBeginListenWorkList.Reset();
StartListen = false;
}
private void 开始自动监听ToolStripMenuItem_Click(object sender, EventArgs e)
{
this.开始自动监听ToolStripMenuItem.Enabled = false;
this.停止自动监听ToolStripMenuItem.Enabled = true;
_eventBeginListenWorkList.Set(); // 2.手动通过Set发送信号恢复线程，让其工作
StartListen = true;
}
3.现在我们需要定义RequestHandler来指定ResourceHandler拦截ajax请求
private void Form1_Load(object sender, EventArgs e)
{
chromiumWebBrowser1.RequestHandler = new MyRequestHandler(this);
chromiumWebBrowser1.Load("https://www.xxxxxxxx.com/");
}
MyRequestHandler中需要指定自定义ResourceHandler
public class MyRequestHandler : RequestHandler
{
Form1 _form;
public MyRequestHandler(Form1 form)
{
_form = form;
}
public static string AuthorizationValue;
protected override bool OnBeforeBrowse(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, bool userGesture,
bool isRedirect)
{
// 先调用基类的实现，断点调试
return base.OnBeforeBrowse(chromiumWebBrowser, browser, frame, request, userGesture, isRedirect);
}
protected override IResourceRequestHandler GetResourceRequestHandler(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame,
IRequest request, bool isNavigation, bool isDownload, string requestInitiator, ref bool disableDefaultHandling)
{
Console.WriteLine(request.Url);
if (request.Url.StartsWith("https://www.xxxxxxxxxxxxxxxx/api") && request.Headers.AllKeys.Contains("Authorization"))
{
AuthorizationValue = request.Headers["Authorization"];
}
return new MyResourceRequestHandler(_form);
}
}
4.最后ResourceRequestHandler拦截到ajax请求之后，如果结果不是AVALIABLE则通过StartListenFunc再次恢复线程
public class MyResourceRequestHandler : ResourceRequestHandler
{
Form1 _form;
public MyResourceRequestHandler(Form1 form)
{
_form = form;
}
private Dictionary<ulong, MemoryStreamResponseFilter> responseDictionary = new Dictionary<ulong, MemoryStreamResponseFilter>();
protected override IResponseFilter GetResourceResponseFilter(IWebBrowser browserControl, IBrowser browser, IFrame frame, IRequest request, IResponse response)
{
var dataFilter = new MemoryStreamResponseFilter();
responseDictionary.Add(request.Identifier, dataFilter);
return dataFilter;
}
protected override void OnResourceLoadComplete(IWebBrowser browserControl, IBrowser browser, IFrame frame, IRequest request, IResponse response, UrlRequestStatus status, long receivedContentLength)
{
MemoryStreamResponseFilter filter;
if (responseDictionary.TryGetValue(request.Identifier, out filter))
{
var data = filter.Data;
if (request.Url.StartsWith("https://xxxxxxxxxxxxxxxxxxxx/oneapi"))
{
var available = false;
string s = System.Text.Encoding.UTF8.GetString(data, 0, data.Length);
Console.WriteLine(s);
if (!string.IsNullOrEmpty(s))
{
var responseData = JsonConvert.DeserializeObject<ScheduleResponse>(s);
if (responseData != null && responseData.productPreviews != null)
{
foreach (var item in responseData.productPreviews)
{
if (item.schedule != null && item.schedule.status != null && item.schedule.status.name == "AVAILABLE")
{
available = true;
Mp3Player.Play();
Action act = delegate () { _form.StopListen(); };
_form.Invoke(act);
break;
}
}
}
}
if (!available && Form1.StartListen)
{
Form1.StartListenFunc();
}
}
filter.Dispose();
}
}
}
而StartListenFunc则是通过Set方法再次恢复了线程对ui的重复查询
public static void StartListenFunc()
{
_eventBeginListenWorkList.Set();
StartListen = true;
}
ManualResetEvent官方介绍如下
https://docs.microsoft.com/zh-cn/dotnet/api/system.threading.manualresetevent?view=netframework-1.1
