如何为不接受取消令牌的异步函数设置超时？ [英] How can I set a timeout for an Async function that doesn't accept a cancellation token?

问题描述

我的Web请求由此代码处理；

I have my web requests handled by this code;

Response = await Client.SendAsync(Message, HttpCompletionOption.ResponseHeadersRead, CToken);

在读取响应标头之后和内容读取完成之前返回。当我调用此行获取内容时……

That returns after the response headers are read and before the content is finished reading. When I call this line to get the content...

return await Response.Content.ReadAsStringAsync();

我希望能够在X秒后停止它。但是它不接受取消令牌。

I want to be able to stop it after X seconds. But it doesn't accept a cancellation token.

推荐答案

尽管您可以依靠 WithCancellation 用于重用，一个更简单的超时解决方案（不会抛出 OperationCanceledException ）将是使用以下方法创建超时任务 Task.Delay 并使用 Task.WhenAny ：

While you can rely on WithCancellation for reuse purposes, a simpler solution for a timeout (which doesn't throw OperationCanceledException) would be to create a timeout task with Task.Delay and wait for the first task to complete using Task.WhenAny:

public static Task<TResult> WithTimeout<TResult>(this Task<TResult> task, TimeSpan timeout)
{
    var timeoutTask = Task.Delay(timeout).ContinueWith(_ => default(TResult), TaskContinuationOptions.ExecuteSynchronously);
    return Task.WhenAny(task, timeoutTask).Unwrap();
}

或者，如果您想抛出异常，以防超时而不是只是返回默认值（即 null ）：

Or, if you want to throw an exception in case there's a timeout instead of just returning the default value (i.e. null):

public static async Task<TResult> WithTimeout<TResult>(this Task<TResult> task, TimeSpan timeout)
{
    if (task == await Task.WhenAny(task, Task.Delay(timeout)))
    {
        return await task;
    }
    throw new TimeoutException();
}

用法为：

var content = await Response.Content.ReadAsStringAsync().WithTimeout(TimeSpan.FromSeconds(1));

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