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This article mainly explains "C#multi-thread example analysis". The explanation content in this article is simple and clear, easy to learn and understand. Please follow the ideas of Xiaobian slowly and deeply to study and learn "C#multi-thread example analysis" together.

A thread is the smallest unit of computing that an operating system can schedule. It is contained within the process and is the actual operational unit within the process. A thread refers to a single sequential flow of control in a process, and multiple threads can be concurrent in a process, each thread executing different tasks in parallel. Process is the basic unit of resource allocation. All resources associated with the process are recorded in the process control block PCB. To indicate that the process owns these resources or is using them.

synchronized manner

Business scenario: Users click a button and do a time-consuming business. The synchronization mode code is as follows:

private void btnSync_Click(object sender, EventArgs e){ Stopwatch watch = Stopwatch.StartNew(); watch.Start(); Console.WriteLine("***********btnSync_Click synchronization method start, Thread ID= {0}*******", Thread.CurrentThread.ManagedThreadId); for (int i = 0; i

< 5; i++) { string name = string.Format("{0}_{1}", "btnSync_Click", i); this.DoSomethingLong(name); } Console.WriteLine("************btnSync_Click同步方法 结束，线程ID= {0}************", Thread.CurrentThread.ManagedThreadId); watch.Stop(); Console.WriteLine("************总耗时= {0}************", watch.Elapsed.TotalSeconds.ToString("0.00"));}/// /// 模拟做一些长时间的工作/// /// private void DoSomethingLong(string name){ Console.WriteLine("************DoSomethingLong 开始 name= {0} 线程ID= {1} 时间 = {2}************", name, Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:mm:ss.fff")); //CPU计算累加和 long rest = 0; for (int i = 0; i < 1000000000; i++) { rest += i; } Console.WriteLine("************DoSomethingLong 结束 name= {0} 线程ID= {1} 时间 = {2} 结果={3}************", name, Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:mm:ss.fff"), rest);} 同步方式输出结果，如下所示：

From the analysis of the above examples, the following conclusions can be drawn:

The synchronous mode is executed sequentially.

Synchronized mode Business and UI adopt the same thread, both of which are main threads.

If the operation takes time to perform, the front-end UI will get stuck and cannot respond to user requests.

Comparison of synchronization methods [9.32 seconds in this example]

asynchronous multithreading mode

How to optimize synchronization mode problems? The answer is to change from synchronous mode to asynchronous multithreading mode. The code is as follows:

private void btnAsync_Click(object sender, EventArgs e){ Stopwatch watch = Stopwatch.StartNew(); watch.Start(); Console.WriteLine("***********btnAsync_Click asynchronous method start, Thread ID= {0}*******", Thread.CurrentThread.ManagedThreadId); Action action = new Action(DoSomethingLong); for (int i = 0; i

< 5; i++) { string name = string.Format("{0}_{1}", "btnAsync_Click", i); action.BeginInvoke(name,null,null); } Console.WriteLine("************btnAsync_Click异步方法 结束，线程ID= {0}************", Thread.CurrentThread.ManagedThreadId); watch.Stop(); Console.WriteLine("************总耗时= {0}************", watch.Elapsed.TotalSeconds.ToString("0.00"));} 异步方式出结果，如下所示：

From the analysis of the above examples, the following conclusions can be drawn:

Asynchronous mode is not sequential execution, that is, it has disorder.

Asynchronous mode adopts multi-thread mode, and UI is not the same thread, so front-end UI will not get stuck.

Asynchronous multithreading mode has short execution time and fast response speed.

By observing the task manager, it is found that synchronous mode consumes more time, asynchronous mode consumes more resources (this example is CPU-intensive operation), and it belongs to resource exchange for performance. CPU utilization for synchronous and asynchronous modes is shown in the following figure:

Asynchronous multithreading optimization

Through the above example, it is found that due to asynchronous reasons, the thread has not ended, but the statement behind is executed first, so the total execution time of the statistical program is 0 seconds. To optimize this problem, use async and await combination execution, the code is as follows:

private async void btnAsync2_Click(object sender, EventArgs e){ Stopwatch watch = Stopwatch.StartNew(); watch.Start(); Console.WriteLine("***********btnAsync_Click2 asynchronous method start, Thread ID= {0}*******", Thread.CurrentThread.ManagedThreadId); await DoAsync(); Console.WriteLine("***********btnAsync_Click2 asynchronous method end, Thread ID= {0}*******", Thread.CurrentThread.ManagedThreadId); watch.Stop(); Console.WriteLine("********** Total elapsed time = {0}********", watch.Elapsed.TotalSeconds.ToString("0.00"));}// ///asynchronous method//// private async Task DoAsync() { Action action = new Action(DoSomethingLong); List results = new List(); for (int i = 0; i

< 5; i++) { string name = string.Format("{0}_{1}", "btnAsync_Click", i); IAsyncResult result = action.BeginInvoke(name, null, null); results.Add(result); } await Task.Run(()=>

{ while (true) { for (int i = 0; i

< results.Count; i++) { var result = results[i]; if (result.IsCompleted) { results.Remove(result); break; } } if (results.Count < 1) { break; } Thread.Sleep(200); } });} 经过优化，执行结果如下所示： 通过异步多线程优化后的执行结果，进行分析后得出的结论如下： Action的BeginInvoke，会返回IAsyncResult接口，通过接口可以判断是否完成。 如果有多个Action的多线程调用，可以通过List方式进行。 async与await组合，可以实现异步调用，防止线程阻塞。 通过以上方式，采用异步多线程的方式，共耗时3.26秒，比同步方式的9.32秒，提高了2.85倍，并非线性增加。且每次执行的总耗时会上下浮动，并非固定值。 异步回调 上述async与await组合，是一种实现异步调用的方式，其实Action本身也具有回调函数【AsyncCallback】，通过回调函数一样可以实现对应功能。具体如下所示： /// /// 异步回调/// /// /// private void btnAsync3_Click(object sender, EventArgs e){ Stopwatch watch = Stopwatch.StartNew(); watch.Start(); Console.WriteLine("************btnAsync_Click3异步方法 开始，线程ID= {0}************", Thread.CurrentThread.ManagedThreadId); Action action = DoAsync3; AsyncCallback asyncCallback = new AsyncCallback((ar) =>

{ if (ar.IsCompleted) { Console.WriteLine("***********btnAsync_Click3 asynchronous method end, Thread ID= {0}*******", Thread.CurrentThread.ManagedThreadId); watch.Stop(); Console.WriteLine("********** Total elapsed time = {0}********", watch.Elapsed.TotalSeconds.ToString("0.00")); } }); action.BeginInvoke(asyncCallback, null);}private void DoAsync3(){ Action action = new Action(DoSomethingLong); List results = new List(); for (int i = 0; i

< 5; i++) { string name = string.Format("{0}_{1}", "btnAsync_Click3", i); IAsyncResult result = action.BeginInvoke(name, null, null); results.Add(result); } while (true) { for (int i = 0; i < results.Count; i++) { var result = results[i]; if (result.IsCompleted) { results.Remove(result); break; } } if (results.Count < 1) { break; } Thread.Sleep(200); }} 异步回调执行示例，如下所示： 通过对异步回调方式执行结果进行分析，结论如下所示： 通过观察线程ID可以发现，由于对循环计算的功能进行了封装，为一个独立的函数，所以在Action通过BeginInvoke发起时，又是一个新的线程。 通过async和await在通过Task.Run方式返回时，也会重新生成新的线程。 通过回调函数，可以保证异步线程的执行顺序。 通过Thread.Sleep(200)的方式进行等待，会有一定时间范围延迟。 异步信号量 信号量方式是通过BeginInvoke返回值IAsyncResult中的异步等待AsyncWaitHandle触发信号WaitOne，可以实现信号的实时响应，具体代码如下： private void btnAsync4_Click(object sender, EventArgs e){ Stopwatch watch = Stopwatch.StartNew(); watch.Start(); Console.WriteLine("************btnAsync_Click4异步方法 开始，线程ID= {0}************", Thread.CurrentThread.ManagedThreadId); Action action = DoAsync3; var asyncResult = action.BeginInvoke(null, null); //此处中间可以做其他的工作，然后在最后等待线程的完成 asyncResult.AsyncWaitHandle.WaitOne(); Console.WriteLine("************btnAsync_Click4异步方法 结束，线程ID= {0}************", Thread.CurrentThread.ManagedThreadId); watch.Stop(); Console.WriteLine("************总耗时= {0}************", watch.Elapsed.TotalSeconds.ToString("0.00"));} 信号量示例截图如下所示： 通过对异步信号量方式的测试结果进行分析，得出结论如下： 信号量方式会造成线程的阻塞，且会造成前端界面卡死。 信号量方式适用于异步方法和等待完成之间还有其他工作需要处理的情况。 WaitOne可以设置超时时间【最多可等待时间】。 异步多线程返回值 上述示例的委托都是无返回值类型的，那么对于有返回值的函数，如何获取呢？答案就是采用Func。示例如下所示： private void btnAsync5_Click(object sender, EventArgs e){ Stopwatch watch = Stopwatch.StartNew(); watch.Start(); Console.WriteLine("************btnAsync5_Click异步方法 开始，线程ID= {0}************", Thread.CurrentThread.ManagedThreadId); string name = string.Format("{0}_{1}", "btnAsync_Click5", 0); Func func = new Func(DoSomethingLongAndReturn); IAsyncResult asyncResult = func.BeginInvoke(name, null, null); //此处中间可以做其他的工作，然后在最后等待线程的完成 int result = func.EndInvoke(asyncResult); Console.WriteLine("************btnAsync5_Click异步方法 结束，线程ID= {0}，返回值={1}************", Thread.CurrentThread.ManagedThreadId,result); watch.Stop(); Console.WriteLine("************总耗时= {0}************", watch.Elapsed.TotalSeconds.ToString("0.00"));}private int DoSomethingLongAndReturn(string name){ Console.WriteLine("************DoSomethingLong 开始 name= {0} 线程ID= {1} 时间 = {2}************", name, Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:mm:ss.fff")); //CPU计算累加和 long rest = 0; for (int i = 0; i < 1000000000; i++) { rest += i; } Console.WriteLine("************DoSomethingLong 结束 name= {0} 线程ID= {1} 时间 = {2} 结果={3}************", name, Thread.CurrentThread.ManagedThreadId, DateTime.Now.ToString("HH:mm:ss.fff"), rest); return DateTime.Now.Day;} 采用Func方式的EndInvoke，可以获取返回值，示例如下： 通过对Func方式的EndInvoke方法的示例进行分析，得出结论如下所示： 在主线程中调用EndInvoke，会进行阻塞，前端页面卡死。 Func的返回值是泛型类型，可以返回任意类型的值。 异步多线程返回值回调 为了解决以上获取返回值时，前端页面卡死的问题，可以采用回调函数进行解决，如下所示： private void btnAsync6_Click(object sender, EventArgs e){ Stopwatch watch = Stopwatch.StartNew(); watch.Start(); Console.WriteLine("************btnAsync6_Click异步方法 开始，线程ID= {0}************", Thread.CurrentThread.ManagedThreadId); string name = string.Format("{0}_{1}", "btnAsync_Click6", 0); Func func = new Func(DoSomethingLongAndReturn); AsyncCallback callback = new AsyncCallback((asyncResult) =>

{ int result = func.EndInvoke(asyncResult); Console.WriteLine("***********btnAsync6_Click asynchronous method end, Thread ID= {0}, return value ={1}********", Thread.CurrentThread.ManagedThreadId, result); watch.Stop(); Console.WriteLine("********** Total elapsed time = {0}********", watch.Elapsed.TotalSeconds.ToString("0.00")); }); func.BeginInvoke(name, callback, null);}

Using callback mode, the example screenshot is as follows:

By analyzing examples of callback methods, the following conclusions can be drawn:

EndInvoke is called in the asynchronous callback function and can be returned directly without blocking.

Asynchronous callback mode, front-end UI thread is no longer stuck.

Thank you for reading, the above is "C#multi-thread example analysis" content, after the study of this article, I believe we have a deeper understanding of C#multi-thread example analysis, the specific use of the situation also needs to be verified. Here is, Xiaobian will push more articles related to knowledge points for everyone, welcome to pay attention!

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