Wait()导致UI线程挂起-什么时候应使用Wait()? [英] Wait() causes UI thread to hang - when should Wait() be used?

问题描述

我有以下代码连接到SignalR集线器

I have the following code that connects to a SignalR Hub

    private static async Task StartListening()
    {
        try
        {


            var hubConnection = new HubConnection("http://localhost:8080/");                
            IHubProxy hubProxy = hubConnection.CreateHubProxy("Broadcaster");
            hubProxy.On<EventData>("notifyCardAccessEvent", eventData =>
            {
                Log.Info(string.Format("Incoming data: {0} {1}", eventData.Id, eventData.DateTime));
            });
            ServicePointManager.DefaultConnectionLimit = 10;
            await hubConnection.Start();
            Log.Info("Connected");
        }
        catch (Exception ex)
        {
            Log.Error(ex);
        }
    }

在我的Form_Load方法中，我有这个

In my Form_Load method, I have this

StartListening();

但是，Resharper提示我考虑将'await'运算符应用于呼叫结果"

However, Resharper prompts me to "consider applying the 'await' operator to the result of the call"

所以我做到了:

Log.Info("Connecting to SignalR hub...");
StartListening().Wait();
Log.Info("Connected!");

但是，这导致我的UI线程挂起，并且Connected!从未打印到日志文件中.

However, this causes my UI thread to hang and Connected! is never printed to the log file.

所以我的问题是，什么时候应该使用Wait()?我应该使用Wait()的实例和场景是什么，什么时候不应该使用Wait()?

So my question is, when should I use Wait()? What are the instances and scenarios that I should use Wait(), and when should I not use Wait()?

推荐答案

await不是Wait.目前尚不清楚调用StartListening()的代码是什么，但建议使用await来替代它，

await is not Wait. It is unclear what the code is that is calling StartListening(), but one option is to await it, as suggested:

await StartListening();

但是，在其他一些情况下，最好什么也不做:

However, in some other cases it may be better to do nothing at all:

StartListening(); // drop the Task on the floor

，或者使用ContinueWith进行手动继续.由于StartListening方法会捕获任何异常，因此仅忽略返回的Task并没有什么不妥-因此，您已经拥有了什么.我建议将其命名为StartListeningAsync.

or perhaps use ContinueWith for a manual continuation. Since the StartListening method catches any exceptions, there isn't anything wrong with just ignoring the returned Task - so what you had already. I would suggest calling it StartListeningAsync, though.

发生死锁的原因是，如果使用Wait，则UI线程将阻止等待异步方法完成，但是该异步方法正在捕获同步上下文，这意味着为了处理它尝试的每个连续性进入UI线程-已被阻止...在其上 .

The reason for the deadlock is that if you use Wait, your UI thread blocks waiting on an asynchronous method to complete, but that asynchronous method is capturing the sync-context, which means in order to process each continuation it tries to get onto the UI thread - which is blocked... on it.

这篇关于Wait()导致UI线程挂起-什么时候应使用Wait()?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！