使用.Result的异步方法
本文关键字:异步方法 Result 使用 | 更新日期: 2023-09-27 18:24:45
下面的方法循环遍历postdata列表,对一个令牌发出多个请求,例如每个请求都使用一个特定的clientID。我的问题与异步有关。我正在尝试使令牌的调用是异步的。.Result的使用是否一定会使方法同步?
public async Task<string> ReturnDataFromUrl1(List<List<KeyValuePair<string, string>>> listOfPostData)
{
List<Task<string>> taskList = new List<Task<string>>();
string allTokens = "";
List<Task<string>> downloadTasks = new List<Task<string>>();
foreach (var postData in listOfPostData)
{
using (var client = new HttpClient())
{
client.BaseAddress = new Uri("http://localhost:23081");
HttpContent httpContent = new FormUrlEncodedContent(postData);
HttpResponseMessage response = client.PostAsync("/Token", httpContent).Result;
var responsecode = (int)response.StatusCode;
if (response.IsSuccessStatusCode)
{
var responseBodyAsText = response.Content.ReadAsStringAsync();
taskList.Add(responseBodyAsText);
}
}
}
downloadTasks = taskList.ToList();
while (downloadTasks.Count > 0)
{
Task<string> firstFinishedTask = await Task.WhenAny(downloadTasks);
downloadTasks.Remove(firstFinishedTask);
// Await the completed task.
string content = await firstFinishedTask;
allTokens = allTokens + content;
}
return allTokens;
}
.Result的使用是否一定会使方法同步?
它将使与.Result
同步阻塞的部分同步,因为它同步等待Task
的完成(如果您的代码没有死锁,这在具有自定义SynchronizationContext
的环境中是非常可能的)。
此方法调用:
Task<string> firstFinishedTask = await Task.WhenAny(downloadTasks);
将是异步的,因为它将产生控制,直到第一个流被读取并转换为字符串。如果您已经有一个标记为async
的方法,那么只需await
也可以标记该部分:
HttpResponseMessage response = await client.PostAsync("/Token", httpContent);
旁注:
我想我会对这个问题采取不同的方法。通常情况下,网络IO将消耗该方法最多的时间。如果可能并且没有限制的话,我会同时进行这些网络呼叫,然后处理结果:
public async Task<string> ReturnDataFromUrlAsync(
List<List<KeyValuePair<string, string>>> listOfPostData)
{
var client = new HttpClient
{
BaseAddress = new Uri("http://localhost:23081")
};
var downloadTasks = listOfPostData.Select(postData =>
{
var content = new FormUrlEncodedContent(postData);
return client.PostAsync("/Token", content);
}).ToList();
var tokenBuilder = new StringBuilder(downloadTasks.Count);
while (downloadTasks.Count > 0)
{
var finishedTask = await Task.WhenAny(downloadTasks);
downloadTasks.Remove(finishedTask);
var response = await finishedTask;
if (!response.IsSuccessStatusCode)
continue;
var token = await response.Content.ReadAsStringAsync();
tokenBuilder.Append(token);
}
return tokenBuilder.ToString();
}
或者,由于您需要所有结果才能处理令牌,因此可以使用Task.WhenAll
等待所有结果完成:
public async Task<string> ReturnDataFromUrlAsync(
List<List<KeyValuePair<string, string>>> listOfPostData)
{
var client = new HttpClient
{
BaseAddress = new Uri("http://localhost:23081")
};
var downloadTasks = listOfPostData.Select(postData =>
{
var content = new FormUrlEncodedContent(postData);
return client.PostAsync("/Token", content);
});
HttpResponseMessage[] response = await Task.WhenAll(downloadTasks);
var tokenBuilder = new StringBuilder(response.Length);
foreach (var element in response.Where(message => message.IsSuccessStatusCode))
{
tokenBuilder.Append(await element.Content.ReadAsStringAsync());
}
return tokenBuilder.ToString();
}