最佳答案
HttpClient.GetAsync(…)在使用await/async时从不返回
编辑: 这个问题看起来可能是同样的问题，但没有响应…
在测试用例5中，任务似乎卡在了WaitingForActivation状态。
我在。net 4.5中使用System.Net.Http.HttpClient时遇到了一些奇怪的行为——其中“等待”调用(例如httpClient.GetAsync(...))的结果将永远不会返回。
这只发生在使用新的async/await语言功能和任务API时的特定情况下-当只使用延续时，代码似乎总是工作。
下面是一些重现这个问题的代码——将其放入Visual Studio 11中的一个新的“MVC 4 WebApi项目”中，以公开以下GET端点:
/api/test1
/api/test2
/api/test3
/api/test4
/api/test5 <--- never completes
/api/test6
这里的每个端点返回相同的数据(来自stackoverflow.com的响应头)，除了/api/test5，它永远不会完成。
我是否在HttpClient类中遇到了错误，或者我是否以某种方式误用了API ?
复制代码:
public class BaseApiController : ApiController
{
/// <summary>
/// Retrieves data using continuations
/// </summary>
protected Task<string> Continuations_GetSomeDataAsync()
{
var httpClient = new HttpClient();
var t = httpClient.GetAsync("http://stackoverflow.com", HttpCompletionOption.ResponseHeadersRead);
return t.ContinueWith(t1 => t1.Result.Content.Headers.ToString());
}
/// <summary>
/// Retrieves data using async/await
/// </summary>
protected async Task<string> AsyncAwait_GetSomeDataAsync()
{
var httpClient = new HttpClient();
var result = await httpClient.GetAsync("http://stackoverflow.com", HttpCompletionOption.ResponseHeadersRead);
return result.Content.Headers.ToString();
}
}
public class Test1Controller : BaseApiController
{
/// <summary>
/// Handles task using Async/Await
/// </summary>
public async Task<string> Get()
{
var data = await Continuations_GetSomeDataAsync();
return data;
}
}
public class Test2Controller : BaseApiController
{
/// <summary>
/// Handles task by blocking the thread until the task completes
/// </summary>
public string Get()
{
var task = Continuations_GetSomeDataAsync();
var data = task.GetAwaiter().GetResult();
return data;
}
}
public class Test3Controller : BaseApiController
{
/// <summary>
/// Passes the task back to the controller host
/// </summary>
public Task<string> Get()
{
return Continuations_GetSomeDataAsync();
}
}
public class Test4Controller : BaseApiController
{
/// <summary>
/// Handles task using Async/Await
/// </summary>
public async Task<string> Get()
{
var data = await AsyncAwait_GetSomeDataAsync();
return data;
}
}
public class Test5Controller : BaseApiController
{
/// <summary>
/// Handles task by blocking the thread until the task completes
/// </summary>
public string Get()
{
var task = AsyncAwait_GetSomeDataAsync();
var data = task.GetAwaiter().GetResult();
return data;
}
}
public class Test6Controller : BaseApiController
{
/// <summary>
/// Passes the task back to the controller host
/// </summary>
public Task<string> Get()
{
return AsyncAwait_GetSomeDataAsync();
}
}
