ManualResetEvent实现线程的暂停与恢复

2022-08-18 15:15:48 浏览数 (1)

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

  1. 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
  2. 手动通过Set方法发送开始工作信号
  3. 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
代码语言:javascript复制
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

代码语言:javascript复制
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

代码语言:javascript复制
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

代码语言:javascript复制
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

代码语言:javascript复制
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

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