Task.Delay永不完成 [英] Task.Delay never completing

问题描述

以下代码将永久冻结.

public async Task DoSomethingAsync()
{
    await Task.Delay(2000);
}

private void Button_Click(object sender, RoutedEventArgs e)
{
    DoSomethingAsync().Wait();
    // Task.Delay(2000).Wait();
}

如果我使用注释掉的代码将呼叫切换到DoSomethingAsync，它的行为将与预期的一样.我怀疑嵌套等待会导致死锁，但是我不确定为什么，或者如何解决.

If I switch the call to DoSomethingAsync with the commented out code, it behaves as expected. I suspect that somehow the nested awaits are causing a deadlock, but I'm not sure why, or how to fix it.

推荐答案

假定Button_Click在GUI线程中运行，则您手上会有死锁.

Assuming Button_Click runs in the GUI thread you have a deadlock on your hands.

在任务上使用Wait时，您正在同步阻塞线程，直到任务结束，但是该任务永远不会结束，因为延续(Task.Delay(2000);的完成)也必须在GUI线程上运行(在Wait).

When you use Wait on a task you are synchronously blocking the thread until the task ends, but the task will never end because the continuation (the completion of Task.Delay(2000);) must run on the GUI thread as well (which is blocked on Wait).

您有几种解决方案.使用ConfigureAwait(false)都不捕获GUI线程的SynchronizationContext:

You have several solutions. Either use ConfigureAwait(false) to not capture the GUI thread's SynchronizationContext:

public async Task DoSomethingAsync()
{
    await Task.Delay(2000).ConfigureAwait(false);
}

或者(建议使用)async void事件处理程序(这是async void方法的唯一适当位置):

Or (which I recommend) use an async void event handler (which is the only appropriate place for an async void method):

private async void Button_Click(object sender, RoutedEventArgs e)
{
    await DoSomethingAsync();
}

public async Task DoSomethingAsync()
{
    await Task.Delay(2000);
}

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