为什么我在这里看不到 ConfigureAwait(false) 和 ConfigureAwait(true) 之间的区别？ [复制]

Question

我正在尝试为我在async-await 上所做的报告创建概念验证。

我做了一个示例代码

using System;
using System.Threading.Tasks;
using System.Threading;

public class Program
{
    static async Task CreateATaskThatPrintsWhichThread()
    {
        Console.WriteLine("Thread on line right before the bottom await = {0}", Thread.CurrentThread.ManagedThreadId);
        await Task.Run(() => 
        {
            Task.Delay(500);
            Console.WriteLine("Thread on line inside bottom task action = {0}", Thread.CurrentThread.ManagedThreadId);                         
        });
        Console.WriteLine("Thread on line right before the bottom await = {0}", Thread.CurrentThread.ManagedThreadId);
    }

    public static void Main()
    {
        Task.Run(async () =>
        {
            Console.WriteLine("Thread on line right before the bottom await = {0}", Thread.CurrentThread.ManagedThreadId);
            Task printStuff = CreateATaskThatPrintsWhichThread();
            printStuff.ConfigureAwait(true);
            await printStuff;
            Console.WriteLine("Thread on line right before the bottom await = {0}", Thread.CurrentThread.ManagedThreadId);
        }).Wait();
    }
}

我在 .NET Fiddle 上反复运行，结果是零星的：

Thread on line right before the bottom await = 14
Thread on line right before the bottom await = 14
Thread on line inside bottom task action = 28
Thread on line right before the bottom await = 28
Thread on line right before the bottom await = 28


Thread on line right before the bottom await = 28
Thread on line right before the bottom await = 28
Thread on line inside bottom task action = 28
Thread on line right before the bottom await = 28
Thread on line right before the bottom await = 28


Thread on line right before the bottom await = 28
Thread on line right before the bottom await = 28
Thread on line inside bottom task action = 53
Thread on line right before the bottom await = 53
Thread on line right before the bottom await = 28

等等。当我更改为 `printStuff.ConfigureAwait(false);

Thread on line right before the bottom await = 99
Thread on line right before the bottom await = 99
Thread on line inside bottom task action = 87
Thread on line right before the bottom await = 36
Thread on line right before the bottom await = 99

Thread on line right before the bottom await = 45
Thread on line right before the bottom await = 45
Thread on line inside bottom task action = 36
Thread on line right before the bottom await = 36
Thread on line right before the bottom await = 45

Thread on line right before the bottom await = 25
Thread on line right before the bottom await = 25
Thread on line inside bottom task action = 12
Thread on line right before the bottom await = 12
Thread on line right before the bottom await = 25

有人可以告诉我结果“应该”是什么，或者可以帮助我在 .NET Fiddle 上创建一个更好的示例吗？

（我也很困惑，因为我认为Task.Run里面的行基本上保证在后台线程上执行）

Answer 1

cmets 涵盖了大部分内容，但由于还没有答案，我认为您所追求的答案是您错误地得出结论，.ConfigureAwait(true) 意味着在await 之后，代码将继续在和以前一样。

这是真的在某些情况下，尤其是那些具有某种形式的消息/调度程序循环的情况。在这些情况下，当 pre-continuation 代码完成时，捕获的 SynchronizationContext 用于将请求发送回调度程序 - 当它下一个能够时 - 获取延续并继续在其线程上执行它。循环通常连续快速地旋转，服务于 UI 问题，一旦注册帖子，它将使用其迭代之一来执行延续。

控制台应用程序没有这样的循环，也没有SynchronizationContext，因此执行延续的任务改为排队到线程池中，任何可用的线程都会执行它。您偶尔会很幸运，并以与继续之前相同的线程结束，但这只是偶然。