如何在 .NET 4.0 中“休眠”，直到请求超时或取消

void MyFunc (CancellationToken ct)
{
   //... 
   // simulate some long lasting operation that should be cancelable 
   Thread.Sleep(TimeSpan.FromMilliseconds(10000), ct); 
}

我只是在这里写了博客：

CancelToken and Thread.Sleep

总之：

var cancelled = token.WaitHandle.WaitOne(TimeSpan.FromSeconds(5));

在您的上下文中：

void MyFunc (CancellationToken ct)
{
   //... 
   // simulate some long lasting operation that should be cancelable 
   var cancelled = ct.WaitHandle.WaitOne(TimeSpan.FromSeconds(10));
}

或者，我认为这很清楚：

Task.Delay(waitTimeInMs, cancellationToken).Wait(cancellationToken);

要在一定时间后取消异步操作，同时仍能够手动取消操作，请使用如下所示的内容

CancellationTokenSource cts = new CancellationTokenSource();
CancellationToken token = cts.Token;
cts.CancelAfter(5000);

这将导致五秒钟后取消。要取消操作，您所要做的就是将token传递到异步方法并使用 token.ThrowifCancellationRequested() 方法，您可以在某处设置一个事件处理程序来触发cts.Cancel()。

所以一个完整的例子是：

CancellationTokenSource cts = new CancellationTokenSource();
CancellationToken token = cts.Token;
cts.CancelAfter(5000);
// Set up the event handler on some button.
if (cancelSource != null)
{
    cancelHandler = delegate
    {
        Cancel(cts);
    };
    stopButton.Click -= cancelHandler;
    stopButton.Click += cancelHandler;
}
// Now launch the method.
SomeMethodAsync(token);

其中stopButton是您单击以取消正在运行的任务的按钮

private void Cancel(CancellationTokenSource cts)
{
    cts.Cancel();
}

并且该方法定义为

SomeMethodAsync(CancellationToken token)
{
    Task t = Task.Factory.StartNew(() => 
        {
            msTimeout = 5000;
            Pump(token);
        }, token,
           TaskCreationOptions.None,
           TaskScheduler.Default);
}

现在，为了使您能够处理线程并启用用户取消，您需要编写一个"抽水"方法

int msTimeout;
bool timeLimitReached = false;
private void Pump(CancellationToken token)
{
    DateTime now = DateTime.Now;
    System.Timer t = new System.Timer(100);
    t.Elapsed -= t_Elapsed;
    t.Elapsed += t_Elapsed;
    t.Start();
    while(!timeLimitReached)
    {
        Thread.Sleep(250);
        token.ThrowIfCancellationRequested();
    }
}
void t_Elapsed(object sender, ElapsedEventArgs e)
{
    TimeSpan elapsed = DateTime.Now - this.readyUpInitialised;
    if (elapsed > msTimeout)
    {
        timeLimitReached = true;
        t.Stop();
        t.Dispose();
    }
}

请注意，SomeAsyncMethod将返回给调用方。要阻止呼叫者，您必须在呼叫层次结构中向上移动Task。

CancelToken.WaitHandle 在 CancelTokenSource 被释放后访问时可能会引发异常：

ObjectDisposedException：CancelTokenSource 已被处置。

在某些情况下，尤其是当链接的取消源被手动处理时（它们应该如此），这可能会令人讨厌。

此扩展方法允许"安全取消等待";但是，它应与取消令牌的状态和/或返回值的用法的检查和正确标记结合使用。这是因为它禁止访问 WaitHandle 的异常，并且返回速度可能比预期快。

internal static class CancellationTokenExtensions
{
    /// <summary>
    /// Wait up to a given duration for a token to be cancelled.
    /// Returns true if the token was cancelled within the duration
    /// or the underlying cancellation token source has been disposed.
    /// </summary>
    public static bool WaitForCancellation(this CancellationToken token, TimeSpan duration)
    {
        WaitHandle handle;
        try
        {
            handle = token.WaitHandle;
        }
        catch
        {
            /// The source of the token was disposed (already cancelled)
            return true;
        }
        if (handle.WaitOne(duration))
        {
            /// A cancellation occured during the wait
            return true;
        }
        else
        {
            /// No cancellation occured during the wait
            return false;
        }
    }
}

到目前为止，我找到的最佳解决方案是：

void MyFunc(CancellationToken ct)
{
  //...
  var timedOut = WaitHandle.WaitAny(new[] { ct.WaitHandle }, TimeSpan.FromMilliseconds(2000)) == WaitHandle.WaitTimeout;
  var cancelled = ! timedOut;
}

更新：

到目前为止，最好的解决方案是公认的答案。