Task.WhenAll()-是否创建新线程?

问题描述

根据 MSDN :

调用Task.WhenAll()时，它会创建一个任务，但这是否必然意味着它会创建一个新线程来执行该任务?例如，在下面的此控制台应用程序中创建了多少个线程?

When Task.WhenAll() is called, it creates a task but does that necessarily mean that it creates a new thread to execute that task? For example, how many threads are created in this console application below?

class Program
{
    static void Main(string[] args)
    {
        RunAsync();
        Console.ReadKey();
    }

    public static async Task RunAsync()
    {

        Stopwatch sw = new Stopwatch();
        sw.Start();
        Task<string> google = GetString("http://www.google.com");
        Task<string> microsoft = GetString("http://www.microsoft.com");
        Task<string> lifehacker = GetString("http://www.lifehacker.com");
        Task<string> engadget = GetString("http://www.engadget.com");

        await Task.WhenAll(google, microsoft, lifehacker, engadget);
        sw.Stop();
        Console.WriteLine("Time elapsed: " + sw.Elapsed.TotalSeconds);
    }

    public static async Task<string> GetString(string url)
    {
        using (var client = new HttpClient())
        {
            return await client.GetStringAsync(url);
        }
    }
}

推荐答案

WhenAll不会创建新线程.一个任务"并不一定意味着一个线程.任务有两种类型:事件"任务(例如TaskCompletionSource)和代码"任务(例如Task.Run). WhenAll是事件样式的任务，因此它不表示代码.如果您是async的新手，建议您从我的入门博客文章开始

WhenAll does not create a new thread. A "task" does not necessarily imply a thread; there are two types of tasks: "event" tasks (e.g., TaskCompletionSource) and "code" tasks (e.g., Task.Run). WhenAll is an event-style task, so it does not represent code. If you're new to async, I recommend starting with my introductory blog post.

您的测试应用程序将根据需要使用线程池线程和IOCP线程来完成async方法，因此它可能仅以2个线程或最多5个线程运行.可以，您可以查看我的有关async线程的最新博客帖子.

Your test application will use thread pool threads and IOCP threads as necessary to finish the async methods, so it may run with as few as 2 threads or as many as 5. If you're curious about how exactly the threading works, you can check out my recent blog post on async threads.

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