如何为延迟的任务增加时间？

Question

我有一个启动FileSystemWatcher的过程，以监视文件系统中的传入文件。

我使用Task.Delay设置了一个延迟，该延迟在设置取消令牌时或在时间到期后（例如10分钟）取消FSW。

watcher.EnableRaisingEvents = true;

// start the timer
RunAfterDelay(TimeSpan.FromMinutes(10), cts.Token, () =>
{
    // get rid of the watcher
    watcher.Dispose();
});

private async void RunAfterDelay(TimeSpan delay, CancellationToken token, Action action)
{
    await Task.Delay(delay, token);
    if (!token.IsCancellationRequested)
    {
        action();
    }
}

但是我想以某种方式配置它，以便每次出现新文件时都可以添加额外的延迟。 如此有效地某种滑动到期延迟。

Answer 1

您可以略微更改您的延迟方法，以便能够改变执行时间。

我为您创建了一个小示例。

然后，您可以通过一种简单的方法对FileSystemWatcher进行“延迟处理”：

CancellationTokenSource cts = new CancellationTokenSource();
await watcher.DisposeDelayed(TimeSpan.FromSeconds(10), cts.Token);

我为FileSystemWatcher创建了一个扩展方法DisposeDelayed ：

static class Utilities
{
    public static async Task DisposeDelayed(this FileSystemWatcher watcher, TimeSpan inactivePeriod, CancellationToken ct)
    {
        DateTime disposalTime = DateTime.Now + inactivePeriod;
        FileSystemEventHandler postponeTrigger = (s, e) => disposalTime = DateTime.Now + inactivePeriod;
        watcher.Created += postponeTrigger;
        watcher.Changed += postponeTrigger;
        // add here other event handlers you need to postpone the disposal

        try
        {
            await RunAtTimePoint(() => disposalTime, ct, watcher.Dispose).ConfigureAwait(false);
        }
        finally
        {
            // don't forget to unsubscribe from each event
            watcher.Created -= postponeTrigger;
            watcher.Changed -= postponeTrigger;
        }
    }

    // You can also use this method for other tasks if you need
    public static async Task RunAtTimePoint(Func<DateTime> execTimeProvider, CancellationToken token, Action action)
    {
        int delayTime;
        do
        {
            // first, calculate the time left until the execution
            DateTime execTime = execTimeProvider();
            TimeSpan timeLeft = execTime - DateTime.Now;

            // we delay in 1000 ms chunks;
            // but if the delay time is less, we need to handle that
            delayTime = (int)Math.Min(1000d, timeLeft.TotalMilliseconds);
            if (delayTime > 0)
            {
                // don't forget the ConfigureAwait call:
                // we don't need the context switch each time
                await Task.Delay(delayTime, token).ConfigureAwait(false);
            }
        }
        while (delayTime > 0 && !token.IsCancellationRequested);

        if (!token.IsCancellationRequested)
        {
            action();
        }
    }
}