如何返回等待调度程序线程中的事件的等待(任务?) [英] How to return awaitable (Task?) that waits for an event in Dispatcher Thread

问题描述

我有主题:

1. 具有Dispatcher循环的UI线程
2. 在排队框架中侦听消息的后台线程.

收到消息后，将在后台线程中触发一个事件:

when a message is received, an event is fired in the background thread:

messageReceiver.Received += (sender, args) => ...

在UI线程中，我想等待一条消息，如下所示:

In UI thread I would like to await a message, something like this:

void ButtonClicked(object sender, RoutedEventArgs e) {
    await NextMessage(); //should return when messageReceiver.Received is fired
}

如何实现等待的NextMessage方法，这样它就不会每次都创建新线程?

有一个SemaphoreSlim类，我可以等待WaitAsync，但似乎会创建一个新线程，该线程在释放SemaphoreSlim之前会被阻塞.

There is SemaphoreSlim class where I can await WaitAsync, but is seems to create new thread that is blocked until SemaphoreSlim is released.

也许TaskCompletionSource是要走的路?那我应该使用哪个TaskCreationOption?

Maybe TaskCompletionSource is the way to go? Which TaskCreationOption should I use then?

推荐答案

您提到了TaskCompletionSource，我认为这就是您所需要的.您可以将其绑定到.Received事件，如下所示:

You mentioned the TaskCompletionSource and that is what I believe you need here. You'd tether it to the .Received event like so:

static Task<IEnumerable<Message>> FromEvent(Receiver messageReceiver)
{
    var tcs = new TaskCompletionSource<IEnumerable<Message>>();

    EventHandler<IEnumerable<Message>> handler = null;
    handler = (o, e) =>
        {
            messageReceiver.Received -= handler;
            tcs.SetResult(e.Messages);
        };
    messageReceiver.Received += handler;

    return tcs.Task;
}

然后您可以像这样等待它:

Then you could await it like this:

// Having the async keyword is fine here since this is an event handler 
async void ButtonClicked(object sender, RoutedEventArgs e) 
{
    var messages = await FromEvent(messageReceiver);
}

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