与Task一起编辑UI的task.Wait()上的死锁 [英] DeadLock on task.Wait() with Task which edit UI

问题描述

我正在尝试为我的问题找到一些解决方案，但是没有结果(或者我只是没有正确地解决问题)，因此，如果有人可以帮助/解释我，我将非常感激.

I'm trying to find some solutions to my problem here, but with no result (or I just do not get them right) so if anyone could help / explain i will be really gratefull.

我正在为使用Win Form的系统管理员开发工具，现在我需要在后台运行的所选计算机上创建一个连续的ping.UI上有一个在线状态指示器，我需要使用背景ping进行编辑.所以现在我处于这种状态:

I'm just developing a tool for system administrators using Win Form and now I need to create a continuous ping on the selected machine which is running on the background. There is an indicator for Online status on UI which I need to edit with background ping. So right now I'm in this state:

A类(获胜表格):

ClassB activeRelation = new ClassB();

public void UpdateOnline(Relation pingedRelation)
{
    //There is many Relations at one time, but form shows Info only for one...
    if (activeRelation == pingedRelation)
    {
        if (p_Online.InvokeRequired)
        {
            p_Online.Invoke(new Action(() =>
                p_Online.BackgroundImage = (pingedRelation.Online) ? Properties.Resources.Success : Properties.Resources.Failure
            ));
        }
        else
        {
            p_Online.BackgroundImage = (pingedRelation.Online) ? Properties.Resources.Success : Properties.Resources.Failure;
        }
    }
}

//Button for tunring On/Off the background ping for current machine
private void Btn_PingOnOff_Click(object sender, EventArgs e)
{
    Button btn = (sender is Button) ? sender as Button : null;

    if (btn != null)
    {
        if (activeRelation.PingRunning)
        {
            activeRelation.StopPing();
            btn.Image = Properties.Resources.Switch_Off;
        }
        else
        {
            activeRelation.StartPing(UpdateOnline);
            btn.Image = Properties.Resources.Switch_On;
        }
    }
}

B类(代表与某台计算机的关系的类)

Class B (class thats represent relation to some machine)

private ClassC pinger;    

public void StartPing(Action<Relation> action)
{
    pinger = new ClassC(this);
    pinger.PingStatusUpdate += action;
    pinger.Start();
}

public void StopPing()
{
    if (pinger != null)
    {
        pinger.Stop();
        pinger = null;
    }
}

C类(后台Ping类)

Class C (background ping class)

private bool running = false;
private ClassB classb;
private Task ping;
private CancellationTokenSource tokenSource;
public event Action<ClassB> PingStatusUpdate;

public ClassC(ClassB classB)
{
    this.classB = classB;
}

public void Start()
{
    tokenSource = new CancellationTokenSource();
    CancellationToken token = tokenSource.Token;

    ping = PingAction(token);
    running = true;
}

public void Stop()
{
    if (running)
    {
        tokenSource.Cancel();
        ping.Wait(); //And there is a problem -> DeadLock
        ping.Dispose();
        tokenSource.Dispose();
    }

    running = false;
}

private async Task PingAction(CancellationToken ct)
{
    bool previousResult = RemoteTasks.Ping(classB.Name);
    PingStatusUpdate?.Invoke(classB);

    while (!ct.IsCancellationRequested)
    {
        await Task.Delay(pingInterval);

        bool newResult = RemoteTasks.Ping(classB.Name);

        if (newResult != previousResult)
        {
            previousResult = newResult;
            PingStatusUpdate?.Invoke(classB);
        }
    }
}

所以当我取消令牌并等待Wait()完成任务时，问题就陷入了僵局->它仍在运行，但是Task中的While(...)正确完成了.

So the problem is in deadlock when I cancel token and Wait() for task to complete -> it's still running, but While(...) in task is finished right.

推荐答案

由于 ping.Wait(); 阻止了UI线程，您陷入了僵局.

You have a deadlock because ping.Wait(); blocks UI thread.

您应该使用 await 异步地等待任务.

You should wait for task asynchronously using await.

因此，如果 Stop()是事件处理程序，则将其更改为:

So, if Stop() is event handler then change it to:

public async void Stop() // async added here
{
    if (running)
    {
        tokenSource.Cancel();
        await ping; // await here
        ping.Dispose();
        tokenSource.Dispose();
    }

    running = false;
}

如果不是:

public async Task Stop() // async added here, void changed to Task
{
    if (running)
    {
        tokenSource.Cancel();
        await ping; // await here
        ping.Dispose();
        tokenSource.Dispose();
    }

    running = false;
}

如 @JohnB 所述，异步方法应具有 Async 后缀，因此，该方法应命名为 StopAsync().

As mentioned by @JohnB async methods should have Async suffix so, the method should be named as StopAsync().

此处说明了类似的问题和解决方案-不阻止异步代码

Similar problem and solution are explained here - Do Not Block On Async Code

您应避免同步等待任务，因此应始终对任务使用 await 而不是 Wait()或 Result .另外，正如 @Fildor 所指出的那样，您应该一直使用 async-await 来避免这种情况.

You should avoid synchronous waiting on tasks, so you should always use await with tasks instead of Wait() or Result. Also, as pointed by @Fildor you should use async-await all the way to avoid such situations.

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