ManualResetEvent实现线程的暂停与恢复

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

        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