等待的作品，但呼吁task.Result挂起/死锁 [英] await works but calling task.Result hangs/deadlocks

问题描述

我有以下四个测试，当我运行它的最后一挂，我的问题是，为什么出现这种情况：

I have the following four tests and the last one hangs when I run it, my question is why this happens:

[Test]
public void CheckOnceResultTest()
{
    Assert.IsTrue(CheckStatus().Result);
}

[Test]
public async void CheckOnceAwaitTest()
{
    Assert.IsTrue(await CheckStatus());
}

[Test]
public async void CheckStatusTwiceAwaitTest()
{
    Assert.IsTrue(await CheckStatus());
    Assert.IsTrue(await CheckStatus());
}

[Test]
public async void CheckStatusTwiceResultTest()
{
    Assert.IsTrue(CheckStatus().Result); // This hangs
    Assert.IsTrue(await CheckStatus());
}

private async Task<bool> CheckStatus()
{
    var restClient = new RestClient(@"https://api.test.nordnet.se/next/1");
    Task<IRestResponse<DummyServiceStatus>> restResponse = restClient.ExecuteTaskAsync<DummyServiceStatus>(new RestRequest(Method.GET));
    IRestResponse<DummyServiceStatus> response = await restResponse;
    return response.Data.SystemRunning;
}

---

我使用这个扩展方法 restsharp RESTClient实现：

public static class RestClientExt
{
    public static Task<IRestResponse<T>> ExecuteTaskAsync<T>(this RestClient client, IRestRequest request) where T : new()
    {
        var tcs = new TaskCompletionSource<IRestResponse<T>>();
        RestRequestAsyncHandle asyncHandle = client.ExecuteAsync<T>(request, tcs.SetResult);
        return tcs.Task;
    }
}

public class DummyServiceStatus
{
    public string Message { get; set; }
    public bool ValidVersion { get; set; }
    public bool SystemRunning { get; set; }
    public bool SkipPhrase { get; set; }
    public long Timestamp { get; set; }
}

为什么最后的测试挂？

Why does the last test hang?

推荐答案

您正在运行，到我描述的对在我的博客和 MSDN文章：在异步法正试图安排其延续到了被阻止通过调用结果。

You're running into the standard deadlock situation that I describe on my blog and in an MSDN article: the async method is attempting to schedule its continuation onto a thread that is being blocked by the call to Result.

在这种情况下，你的的SynchronizationContext 是用于NUnit的执行异步无效测试方法之一。我会尝试使用异步任务的测试方法来代替。

In this case, your SynchronizationContext is the one used by NUnit to execute async void test methods. I would try using async Task test methods instead.

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