ManualResetEvent实现线程的暂停与恢复

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 *** 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 *** 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