Async-await无法正确恢复上下文 [英] Async-await does not recover context correctly

问题描述

我有一个简单的winforms应用程序，它有一个初始化部分，对UI没有任何了解。此初始化运行异步。以下结构显示初始化部分：
$

I've a simple winforms application that has an initialization part that doen't know anything about UI. This initialization runs async. The following contruct shows that initialization part:

[STAThread]
private static void Main()
{
    var main = new Form1();

    using (var mre = new ManualResetEventSlim())
    {
        Initialization().ContinueWith(_ => mre.Set());

        while (!mre.Wait(TimeSpan.FromMilliseconds(25)))
        {
            Application.DoEvents();
        }
    }

    Application.Run(main);
}

private static async Task Initialization()
{
    await Task.Delay(100);
}

我们必须等到初始化才能显示主窗口。我不知道在主要等待异步操作的更好方法 - 欢迎提示。



之后我创建了一个包含以下代码的表单： br $>

We have to wait until initialization before the main window is shown. I don't know a better way to wait for an async operation in main - hints are welcome.

After that I created a form that contains the following code:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private async void Form1_Load(object sender, EventArgs e)
    {
        // Thread.CurrentThread.ManagedThreadId == 1;

        await Task.Delay(500);

        // Thread.CurrentThread.ManagedThreadId != 1 !!!!!!!
    }
}

这就是全部。该表单上没有控件。



问题是Form1_Load开始使用主线程的线程1（如预期的那样）。等待该延迟后，上下文无法正确恢复。等待Task.Delay（100）后运行代码的线程;不是主线。这会导致问题
通过访问该表单中包含的控件。



指定ConfigureAwait（true）将无法解决问题。



如何避免这种情况并强制等待按预期恢复主线程的上下文？



如果我们不出现问题更改以下内容之一：



不要等待使用此hacky构造的异步操作。但是我们需要等待初始化。

在等待构造之后创建Form1的实例。

问题是在Application.Run之前调用Application.DoEvents（） （...）。



程序中强制解决该问题的代码可以简化为：

That's all. There are no controls on that form.

The Problem is that Form1_Load starts using thread 1 (as expected) which is the main thread. After await for that delay the context is not restored correctly. The thread running code after await Task.Delay(100); is not the main thread. That causes problems by accessing controls contained on that form.

Specifying ConfigureAwait(true) will not solve the problem.

How can I avoid that and force await to restore the context as expected to the main thread?

The Problem does not appear if we change one of the following things:

Do not wait for an async operation using this hacky construct. But we need to wait for our initialization.
Create the instance of Form1 after that waiting construct.
The problem is a call of Application.DoEvents() before Application.Run(...).

The code in Program that forces that problem can be simplyfied to:

[STAThread]
private static void Main()
{
    var main = new Form1();
    Application.DoEvents();
    Application.Run(main);
}

初始化（）上的简单Wait（）将导致死锁。

A simple Wait() on Initialization() will result in a deadlock.

推荐答案

如果
初始化不需要表格，然后尝试这个顺序：

If Initialization does not need the form, then try this order:

  
初始化（）。等待（）;

   Initialization().Wait();

  
var main =
new Form1（）;

  
Application.Run（main）;

   Application.Run( main );

 

否则请考虑以下代码：

  
var main =
new Form1（）;

  
Task.Run（初始化）.Wait（）;

   Task.Run( Initialization ).Wait();

  
Application.Run（main）;

   Application.Run( main );

 

这篇关于Async-await无法正确恢复上下文的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！