c# – 在BeginInvoke()中调用异步方法会产生一个’新’线程吗？

线程池中的“新”含义.

鉴于以下示例,我的假设是：

>主方法在一个线程上执行(例如,线程1)
> BeginInvoke使用池中的可用线程来执行AsyncDemo.TestMethod(线程2)
>异步方法调用,例如WebClient.UploadStringAsync使用另一个可用线程(线程3)

第三个是我的问题源于的地方,WebClient.UploadStringAsync的定义：将指定的字符串上传到指定的资源.这些方法不会阻止调用线程.

这是否意味着它使用池中的另一个可用线程？这是一种不明智的技术(异步中的异步)吗？

我的最终目标是异步发布一些数据(触发并忘记),并且之前使用的是UploadStringAsync.现在我决定用BeginInvoke封装周围的代码,但是想一想我是否必须将UploadStringAsync更改为同步方法(UploadString()).

谢谢你的帮助！

public class AsyncMain 
{
    // The delegate will be called asynchronously.
    public delegate string AsyncMethodCaller(out int threadId);

    public static void Main() 
    {       
        // The asynchronous method puts the thread id here.
        int threadId;       

        //Create the delegate.
        AsyncMethodCaller caller = new AsyncMethodCaller(AsyncDemo.TestMethod);

        // Initiate the asychronous call.
        IAsyncResult result = caller.BeginInvoke(out threadId, null, null);     

        Console.WriteLine("In AsyncMain.Main() Thread {0} does some work.", Thread.CurrentThread.ManagedThreadId);

        // Call EndInvoke to wait for the asynchronous call to complete,
        // and to retrieve the results.
        string returnValue = caller.EndInvoke(out threadId, result);

        Console.WriteLine("The async call executed on thread {0}, has responded with \"{1}\". The result is {2}", threadId, returnValue, result);
    }
}


public class AsyncDemo 
{   
    // The method to be executed asynchronously.
    public static string TestMethod(out int threadId) 
    {
        //get threadId, assign it.
        threadId = Thread.CurrentThread.ManagedThreadId;
        Console.WriteLine("TestMethod() begins at thread {0}", threadId);

        //Do work

        //Do ASYNC Method such as: WebClient.UploadStringAsync

        return String.Format("I'm finished my work.");
    }
}

解决方法:

Does this mean it uses another available thread in the pool?

简短回答：是的.

>根据UploadStringAsync的文档：

The string is sent asynchronously using thread resources that are automatically allocated from the thread pool.

>和BeginInvoke uses a thread from the thread pool完成其异步行为.

Is this an ill-advised technique (async within an async)?

如果您需要在两个级别上进行异步行为,那么您可以执行您必须执行的操作.但总的来说,最好的建议是编写最简单的代码,这样就可以使用,所以如果你只能通过一个间接层来逃避,我会说它去做.

遗憾的是,您无法升级到较新版本的.NET,因为对于较新版本,您可以使用任务更简单地完成相同的操作：

public static void Main() 
{       
    Task<string> task = AsyncDemo.TestMethod();

    Console.WriteLine("In AsyncMain.Main() Thread {0} does some work.", Thread.CurrentThread.ManagedThreadId);

    string returnValue = task.Result; // This will cause the main thread to block until the result returns.

    Console.WriteLine("The async call executed on thread {0}, has responded with \"{1}\". The result is {2}", threadId, returnValue, result);
}



public class AsyncDemo 
{   
    // The method to be executed asynchronously.
    public async static Task<string> TestMethod() 
    {
        Console.WriteLine("TestMethod() begins");

        //Do work

        await new WebClient().UploadStringTaskAsync("...", "...");

        return String.Format("I'm finished my work.");
    }
}

标签：c,asynchronous,multithreading,begininvoke
来源： https://codeday.me/bug/20190628/1320741.html