在GetAsync使用的await时的HttpClient没有引发异常 [英] HttpClient not throwing exception when using await on GetAsync

问题描述

我用下面的code得到一个端点，并将其写入到缓存：

I'm using the following code to get an endpoint and write it to a cache:

public async Task UpdateCacheFromHttp(string Uri)
{
    if (string.IsNullOrEmpty(Uri))
        return;

    var httpClient = new HttpClient();
    var response = await httpClient.GetAsync(Uri);

    if ((response != null) && (response.IsSuccessStatusCode))
    {
        var responseStream = await response.Content.ReadAsStreamAsync();
        WriteToCache(responseStream);
    }
}

在code在IIS上运行。

The code is running on IIS.

如果端点不能达到我期望GetAsync抛出异常。即使有一个try-catch，它似乎永远不会失败。 GetAsync永远不会返回（我试过在HttpClient的5秒超时，仍然没有返回）。

If the endpoint can't be reached I'd expect GetAsync to throw an exception. Even with a Try-Catch, it never seems to fail. GetAsync never returns (I tried a 5 second timeout on the HttpClient, still didn't return).

这确实抛出一个异常：

public Task UpdateCacheFromHttp(string Uri)
{
    var updateCacheTask = Task.Factory.StartNew(new Action(() =>
    {
        if (string.IsNullOrEmpty(Uri))
            return;

        var httpClient = new HttpClient();
        var response = httpClient.GetAsync(Uri).Result;

        if (response.IsSuccessStatusCode)
        {
            var responseStream = response.Content.ReadAsStreamAsync().Result;
            WriteToCache(responseStream);
        }
    }));

    return updateCacheTask;
}

我得到预期的无法连接到远程服务器。

I get the expected "Unable to connect to the remote server".

我怀疑它是与IIS中的code运行，但为什么呢？我如何让它正常抛出异常，而无需启动一个新的任务？

I suspect it has something to do with the code running in IIS, but why? How do I get it to properly throw the exception without the need to start a new task?

推荐答案

我的直觉告诉我，你叫等待或结果进一步您的调用堆栈。

My intuition tells me that you're calling Wait or Result further up your call stack.

如果这是正确的，那么你就造成了僵局，为的我在我的博客解释。

If that is correct, then you're causing a deadlock, as I explain on my blog.

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