六种多线程方法解决UI线程堵塞

2024-05-23 21:22:31

{"root":{"nodeName":"document","nodeValue":null,"nodeType":"0","display":"block","nodeAttrs":[],"childNodes":[{"nodeName":"p","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"color: rgb(51, 51, 51);;"}],"childNodes":[{"nodeName":"text","nodeValue":"一、六种多线程方法","nodeType":"3","display":"inline","nodeAttrs":[],"childNodes":[]}]},{"nodeName":"p","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"color: rgb(51, 51, 51);;"}],"childNodes":[{"nodeName":"text","nodeValue":".NET Framework2.0框架提供了至少4种方式实现多线程，它们是“BackgroundWorker”组件、委托的异步调用、线程池ThreadPool以及线程类Thread；.NET Framework 4.0增加了任务并行库TPL和PLINQ技术，可利用Task和并行计算的方法实现。下面列举这6种方法。","nodeType":"3","display":"inline","nodeAttrs":[],"childNodes":[]}]},{"nodeName":"p","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"color: rgb(51, 51, 51);;"}],"childNodes":[{"nodeName":"text","nodeValue":"1. BackgroundWorker组件","nodeType":"3","display":"inline","nodeAttrs":[],"childNodes":[]}]},{"nodeName":"p","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"color: rgb(51, 51, 51);;"}],"childNodes":[{"nodeName":"text","nodeValue":"命名空间：System.ComponentModel","nodeType":"3","display":"inline","nodeAttrs":[],"childNodes":[]}]},{"nodeName":"p","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"color: rgb(51, 51, 51);;"}],"childNodes":[{"nodeName":"text","nodeValue":"程序集：System.dll","nodeType":"3","display":"inline","nodeAttrs":[],"childNodes":[]}]},{"nodeName":"p","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"color: rgb(51, 51, 51);;"}],"childNodes":[{"nodeName":"text","nodeValue":"BackgroundWorker可以用于协助开发WinForm应用程序或WPF应用程序。它作为一个组件发布，提供工作线程的进度反馈、完成事件和取消工作线程方法。在Visual Studio设计器界面里，通过“工具箱”方便地将它加入设计界面，还能通过“属性”窗口设置它的属性和事件。","nodeType":"3","display":"inline","nodeAttrs":[],"childNodes":[]}]},{"nodeName":"p","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"color: rgb(51, 51, 51);;"}],"childNodes":[{"nodeName":"text","nodeValue":"将工作代码写在DoWork事件处理程序里，在主线程（UI线程）调用BackgroundWorker对象的RunWorkerAsync方法即可在一个独立的线程里启动DoWork事件的处理程序。","nodeType":"3","display":"inline","nodeAttrs":[],"childNodes":[]}]},{"nodeName":"div","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"background-color: rgb(231, 229, 220); 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color: rgba(0, 0, 0, 1); background-color: inherit;"}],"childNodes":[{"nodeName":"text","nodeValue":"_tokenSource.Cancel(); ","nodeType":"3","display":"inline","nodeAttrs":[],"childNodes":[]}]}]}]}]}]},{"nodeName":"br","nodeValue":null,"nodeType":"1","display":"inline","nodeAttrs":[],"childNodes":[]},{"nodeName":"br","nodeValue":null,"nodeType":"1","display":"inline","nodeAttrs":[],"childNodes":[]},{"nodeName":"p","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"color: rgb(51, 51, 51);;"}],"childNodes":[{"nodeName":"text","nodeValue":"三、演示","nodeType":"3","display":"inline","nodeAttrs":[],"childNodes":[]}]},{"nodeName":"p","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"color: rgb(51, 51, 51);;"}],"childNodes":[{"nodeName":"text","nodeValue":"在Wrox出版社的《VisualBasic 2005高级编程》第22章有一个求10000内素数的例子讲解.NET的多线程技术，我写了类似的演示代码，演示6种多线程的方法在后台计算素数，而不阻塞UI。","nodeType":"3","display":"inline","nodeAttrs":[],"childNodes":[]}]},{"nodeName":"p","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"color: rgb(51, 51, 51);;"}],"childNodes":[{"nodeName":"img","nodeValue":null,"nodeType":"1","display":"inline","nodeAttrs":[{"attrName":"style","attrValue":" border-style: none;;"},{"attrName":"src","attrValue":"http://hi.csdn.net/attachment/201110/7/0_1318027299Y0JK.gif"}],"childNodes":[]},{"nodeName":"br","nodeValue":null,"nodeType":"1","display":"inline","nodeAttrs":[],"childNodes":[]}]},{"nodeName":"p","nodeValue":null,"nodeType":"1","display":"block","nodeAttrs":[{"attrName":"style","attrValue":"color: rgb(51, 51, 51);;"}],"childNodes":[{"nodeName":"text","nodeValue":"值得一提的是，在任务并发计算素数的演示里，利用CPU多核计算，得到结果所花费的时间有显著的提高。上图中最后一个波峰可看到CPU 0和CPU 1的并行工作情况。","nodeType":"3","display":"inline","nodeAttrs":[],"childNodes":[]}]}]}]},"imageUrls":["https://hi.csdn.net/attachment/201110/7/0_1318027299Y0JK.gif"],"text":"一、六种多线程方法.NET Framework2.0框架提供了至少4种方式实现多线程，它们是“BackgroundWorker”组件、委托的异步调用、线程池ThreadPool以及线程类Thread；.NET Framework 4.0增加了任务并行库TPL和PLINQ技术，可利用Task和并行计算的方法实现。下面列举这6种方法。1. BackgroundWorker组件命名空间：System.ComponentModel程序集：System.dllBackgroundWorker可以用于协助开发WinForm应用程序或WPF应用程序。它作为一个组件发布，提供工作线程的进度反馈、完成事件和取消工作线程方法。在Visual Studio设计器界面里，通过“工具箱”方便地将它加入设计界面，还能通过“属性”窗口设置它的属性和事件。将工作代码写在DoWork事件处理程序里，在主线程（UI线程）调用BackgroundWorker对象的RunWorkerAsync方法即可在一个独立的线程里启动DoWork事件的处理程序。[csharp] backgroundWorker1.RunWorkerAsync(new Parameters(PrimesFrom,PrimesTo)); 若需要在UI上显示工作进度，先使BackgroundWorker对象的WorkerReportsProgress属性设置为True，然后在DoWork事件处理程序里直接用BackgroundWorker对象的ReportProgress方法向UI线程报告工作进度和进度信息，编写BackgroundWorker对象的ProgressChanged事件处理程序，来获得工作进度，更新UI上的进度条等。通常我们还希望点击“取消”按钮，能取消后台工作任务。先使BackgroundWorker对象的WorkerSupportsCancellation属性设置为True，然后在“取消”按钮的单击事件处理程序里直接调用BackgroundWorker对象的CancelAsync方法；在DoWork事件处理程序里，通过BackgroundWorker对象的CancellationPending属性便可得知是否有请求取消操作。[csharp] backgroundWorker1.CancelAsync(); 当DoWork事件处理程序返回后，会在UI线程上产生RunWorkerCompleted事件。2. 委托的异步调用.NET Framework中的许多对象支持同步和异步两种调用方法，它们的异步调用方法名称如BeginXXX。委托也支持同步调用（Invoke）和异步调用（BeginInvoke）两种方式。异步调用是不阻塞当前线程，使委托的方法与调用方代码异步执行；也可以在后台线程里，通过调用支持异步方法的.NET Framework对象（如WinForm的Form对象和WPF的Dispatcher对象）委托的代码，使代码在这些对象所在的线程里执行——这个技巧在后台线程请求执行UI线程上的代码时非常有用。[csharp] if (this.InvokeRequired) //Form1的多线程方法中的代码片段（WPF中也有类似的属性） { varupdate = new Action(TaskCompleted); //调用TaskCompleted方法更新UI this.BeginInvoke(update); } 在当前的类或者一个新类里编写一个后台执行代码的入口方法，然后在UI线程里声明指向此入口方法的委托对象，执行委托对象的BeginInvoke方法即可。委托对象的BeginInvoke方法的参数由两部分组成，第一部分是委托函数的参数，第二部分是委托方法异步调用完成后启动的方法和参数，可以不指定第二部分。[csharp] varworker = new Action(FindPrimesViaDelegate); //委托 worker.BeginInvoke(new Parameters(PrimesFrom,PrimesTo), TaskComplete, null); 从.NET Framework 3.5开始，支持9个传入参数的Action泛型委托和8个传入参数、1个返回值的Func泛型委托，到.NETFramework 4.0，支持传入参数达16个的Action和Func泛型委托。它们被定义在System命名空间，程序集mscorlib.dll，从.NET Framework 3.5时代后，较少的使用Delegate关键字自定义委托了。3. 线程池ThreadPool命名空间：System.Threading程序集：mscorlib.dll每个进程拥有一个线程池。托管代码的线程池的最多支持线程数目与.NET Framework版本及CPU数目等硬件环境有关。在.NET Framework 4.0中，默认每个可用的CPU处理器增加250个辅助线程和1000个I/O线程。可使用SetMaxThreads方法更改线程池的最多线程数（注：承载.NET Framework的非托管代码，如C++，可使用mscoree.h头文件的CorSetMaxThreads函数更改线程池大小）。除了SetMaxThreads方法，还可以使用GetMaxThreads、GetMinThreads、SetMinThreads方法获得或更改线程数。.NET\n Framework中的许多多线程的类或组件（如System.Threading.Timer），就是在线程池中运行的。需要记住一点的是，线程池线程都是后台线程，即线程池线程的IsBackground属性都为True，全部前台线程退出后，线程池线程将被强行中断。用QueueUserWorkItem方法将一个无参数或者仅一个参数的void方法加入到线程池启动。[csharp] ThreadPool.QueueUserWorkItem(FindPrimes, newParameters(PrimesFrom, PrimesTo)); //启动一个线程池线程 4. 线程Thread命名空间：System.Threading程序集：mscorlib.dll将一个无参数或者仅一个参数的void方法委托给Thread实例，调用Thread对象的Start方法启动一个线程，可对它进行优先级、前后台线程、线程单元状态、线程状态及名称等更多细致的控制。[csharp] var t= new Thread(FindPrimes) { Name = \"FindPrimes\", IsBackground = true }; t.Start(new Parameters(PrimesFrom, PrimesTo)); //启动一个线程 5. 任务Task命名空间：System.Threading.Tasks程序集：mscorlib.dllTask作为.NETFramework 4.0推崇的多线程代替办法，方便的控制任务的有序或并行执行，充分地发挥多核CPU性能，将多项任务平衡分配给每个可用的CPU。由于任务中的某些方法使用了数据共享锁技术，可使用Dispose方法显式地销毁这些资源。泛型版本的任务还能取得其返回结果，通常任务作为数组并发执行的。利用Windows任务管理器或性能监视器能监视程序的CPU利用率的波形图。[csharp] _tokenSource= new CancellationTokenSource();//用于取消任务 Task.Factory.StartNew(FindPrimesInTask,new Parameters(PrimesFrom,PrimesTo), _tokenSource.Token); //启动一个任务 6. 并行计算Parallel命名空间：System.Threading.Tasks程序集：mscorlib.dll充分发挥CPU的多核性能，Parallel.Invoke方法可以同时运行多个并行任务，Parallel.For和Parallel.ForEach方法可以并行循环和迭代IEnumerable集合。[csharp] Parallel.For(parameters.Min, parameters.Max, (count, loop) => { //并行执行的代码 //注：在Parallel.For里，第一个参数是min至max的自变量， //第二个参数是指这个并行循环体参数，可执行中断并行循环体等控制方法 } 二、取消线程除了BackgroundWorker组件，在.NETFramework 4.0之前的多线程框架中是不提供类似CancellationToken类型用于支持多线程的取消请求的。常用的办法是轮询检查一个线程间共享的取消标记的方式，获得取消请求，甚至编写一个线程管理器来增强多线程的可控性。.NET Framework4.0对多线程和并行运算进行了增强和改进，CancellationTokenSource对象可以在多线程方案中更有效的发出取消请求。命名空间：System.Threading程序集：mscorlib.dll[csharp] //1.声明一个CancellationTokenSource对象 private CancellationTokenSource _tokenSource; //2.实例化_tokenSource对象 _tokenSource= new CancellationTokenSource(); //3.在支持CancellationToken的代码里判断取消请求 if(_tokenSource.IsCancellationRequested) { loop.Stop(); } //4.在控制线程代码里用调用取消请求 _tokenSource.Cancel(); 三、演示在Wrox出版社的《VisualBasic 2005高级编程》第22章有一个求10000内素数的例子讲解.NET的多线程技术，我写了类似的演示代码，演示6种多线程的方法在后台计算素数，而不阻塞UI。值得一提的是，在任务并发计算素数的演示里，利用CPU多核计算，得到结果所花费的时间有显著的提高。上图中最后一个波峰可看到CPU 0和CPU 1的并行工作情况。"}

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