解决这个问题的另一种方法是使用响应式扩展:

public static Task TimeoutAfter(this Task task, TimeSpan timeout, IScheduler scheduler)
{
        return task.ToObservable().Timeout(timeout, scheduler).ToTask();
}

测试上面使用下面的代码在你的单元测试，它为我工作

TestScheduler scheduler = new TestScheduler();
Task task = Task.Run(() =>
                {
                    int i = 0;
                    while (i < 5)
                    {
                        Console.WriteLine(i);
                        i++;
                        Thread.Sleep(1000);
                    }
                })
                .TimeoutAfter(TimeSpan.FromSeconds(5), scheduler)
                .ContinueWith(t => { }, TaskContinuationOptions.OnlyOnFaulted);

scheduler.AdvanceBy(TimeSpan.FromSeconds(6).Ticks);

您可能需要以下命名空间:

using System.Threading.Tasks;
using System.Reactive.Subjects;
using System.Reactive.Linq;
using System.Reactive.Threading.Tasks;
using Microsoft.Reactive.Testing;
using System.Threading;
using System.Reactive.Concurrency;

创建一个扩展来等待任务或延迟完成，以先发生者为准。如果延迟成功，则抛出异常。

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

下面是一个扩展方法版本，它包含了Andrew Arnott在对他的回答的评论中建议的，当原始任务完成时取消超时。

public static async Task<TResult> TimeoutAfter<TResult>(this Task<TResult> task, TimeSpan timeout) {

    using (var timeoutCancellationTokenSource = new CancellationTokenSource()) {

        var completedTask = await Task.WhenAny(task, Task.Delay(timeout, timeoutCancellationTokenSource.Token));
        if (completedTask == task) {
            timeoutCancellationTokenSource.Cancel();
            return await task;  // Very important in order to propagate exceptions
        } else {
            throw new TimeoutException("The operation has timed out.");
        }
    }
}

安德鲁·阿诺特(Andrew Arnott)回答的几个变体:

If you want to wait for an existing task and find out whether it completed or timed out, but don't want to cancel it if the timeout occurs: public static async Task<bool> TimedOutAsync(this Task task, int timeoutMilliseconds) { if (timeoutMilliseconds < 0 || (timeoutMilliseconds > 0 && timeoutMilliseconds < 100)) { throw new ArgumentOutOfRangeException(); } if (timeoutMilliseconds == 0) { return !task.IsCompleted; // timed out if not completed } var cts = new CancellationTokenSource(); if (await Task.WhenAny( task, Task.Delay(timeoutMilliseconds, cts.Token)) == task) { cts.Cancel(); // task completed, get rid of timer await task; // test for exceptions or task cancellation return false; // did not timeout } else { return true; // did timeout } } If you want to start a work task and cancel the work if the timeout occurs: public static async Task<T> CancelAfterAsync<T>( this Func<CancellationToken,Task<T>> actionAsync, int timeoutMilliseconds) { if (timeoutMilliseconds < 0 || (timeoutMilliseconds > 0 && timeoutMilliseconds < 100)) { throw new ArgumentOutOfRangeException(); } var taskCts = new CancellationTokenSource(); var timerCts = new CancellationTokenSource(); Task<T> task = actionAsync(taskCts.Token); if (await Task.WhenAny(task, Task.Delay(timeoutMilliseconds, timerCts.Token)) == task) { timerCts.Cancel(); // task completed, get rid of timer } else { taskCts.Cancel(); // timer completed, get rid of task } return await task; // test for exceptions or task cancellation } If you have a task already created that you want to cancel if a timeout occurs: public static async Task<T> CancelAfterAsync<T>(this Task<T> task, int timeoutMilliseconds, CancellationTokenSource taskCts) { if (timeoutMilliseconds < 0 || (timeoutMilliseconds > 0 && timeoutMilliseconds < 100)) { throw new ArgumentOutOfRangeException(); } var timerCts = new CancellationTokenSource(); if (await Task.WhenAny(task, Task.Delay(timeoutMilliseconds, timerCts.Token)) == task) { timerCts.Cancel(); // task completed, get rid of timer } else { taskCts.Cancel(); // timer completed, get rid of task } return await task; // test for exceptions or task cancellation }

另一个注释是，如果超时没有发生，这些版本将取消计时器，因此多次调用不会导致计时器堆积。

sjb

这个怎么样:

int timeout = 1000;
var task = SomeOperationAsync();
if (await Task.WhenAny(task, Task.Delay(timeout)) == task) {
    // task completed within timeout
} else { 
    // timeout logic
}

这里有一篇很棒的博客文章“制定任务”。TimeoutAfter Method”(来自MS并行库团队)提供了关于这类事情的更多信息。

补充:在我的回答的评论请求，这里是一个扩展的解决方案，包括取消处理。请注意，将取消传递给任务和计时器意味着在代码中可以经历多种取消方式，您应该确保测试并确信您正确地处理了所有这些方法。不要让各种组合的机会，并希望您的计算机在运行时做正确的事情。

int timeout = 1000;
var task = SomeOperationAsync(cancellationToken);
if (await Task.WhenAny(task, Task.Delay(timeout, cancellationToken)) == task)
{
    // Task completed within timeout.
    // Consider that the task may have faulted or been canceled.
    // We re-await the task so that any exceptions/cancellation is rethrown.
    await task;

}
else
{
    // timeout/cancellation logic
}

使用定时器处理消息并自动取消。当Task完成时，对计时器调用Dispose，以便它们永远不会触发。这里有一个例子;将taskDelay改为500、1500或2500来查看不同的情况:

using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        private static Task CreateTaskWithTimeout(
            int xDelay, int yDelay, int taskDelay)
        {
            var cts = new CancellationTokenSource();
            var token = cts.Token;
            var task = Task.Factory.StartNew(() =>
            {
                // Do some work, but fail if cancellation was requested
                token.WaitHandle.WaitOne(taskDelay);
                token.ThrowIfCancellationRequested();
                Console.WriteLine("Task complete");
            });
            var messageTimer = new Timer(state =>
            {
                // Display message at first timeout
                Console.WriteLine("X milliseconds elapsed");
            }, null, xDelay, -1);
            var cancelTimer = new Timer(state =>
            {
                // Display message and cancel task at second timeout
                Console.WriteLine("Y milliseconds elapsed");
                cts.Cancel();
            }
                , null, yDelay, -1);
            task.ContinueWith(t =>
            {
                // Dispose the timers when the task completes
                // This will prevent the message from being displayed
                // if the task completes before the timeout
                messageTimer.Dispose();
                cancelTimer.Dispose();
            });
            return task;
        }

        static void Main(string[] args)
        {
            var task = CreateTaskWithTimeout(1000, 2000, 2500);
            // The task has been started and will display a message after
            // one timeout and then cancel itself after the second
            // You can add continuations to the task
            // or wait for the result as needed
            try
            {
                task.Wait();
                Console.WriteLine("Done waiting for task");
            }
            catch (AggregateException ex)
            {
                Console.WriteLine("Error waiting for task:");
                foreach (var e in ex.InnerExceptions)
                {
                    Console.WriteLine(e);
                }
            }
        }
    }
}

此外，Async CTP提供了一个TaskEx。Delay方法，它将为您在任务中包装计时器。这可以给你更多的控制来做一些事情，比如设置TaskScheduler为Timer触发时的延续。

private static Task CreateTaskWithTimeout(
    int xDelay, int yDelay, int taskDelay)
{
    var cts = new CancellationTokenSource();
    var token = cts.Token;
    var task = Task.Factory.StartNew(() =>
    {
        // Do some work, but fail if cancellation was requested
        token.WaitHandle.WaitOne(taskDelay);
        token.ThrowIfCancellationRequested();
        Console.WriteLine("Task complete");
    });

    var timerCts = new CancellationTokenSource();

    var messageTask = TaskEx.Delay(xDelay, timerCts.Token);
    messageTask.ContinueWith(t =>
    {
        // Display message at first timeout
        Console.WriteLine("X milliseconds elapsed");
    }, TaskContinuationOptions.OnlyOnRanToCompletion);

    var cancelTask = TaskEx.Delay(yDelay, timerCts.Token);
    cancelTask.ContinueWith(t =>
    {
        // Display message and cancel task at second timeout
        Console.WriteLine("Y milliseconds elapsed");
        cts.Cancel();
    }, TaskContinuationOptions.OnlyOnRanToCompletion);

    task.ContinueWith(t =>
    {
        timerCts.Cancel();
    });

    return task;
}