事件触发后如何重设Task.Delay()? [英] How to reset a Task.Delay() after a event fired?

问题描述

我试图让FileSystemWatcher超过5分钟未收到任何更改后触发一些代码.

I am trying to let some code fire after my FileSystemWatcher hasn't received any changes for more then 5 minutes.

我当前的方法是在更改后调用 await Task.Delay(); ，希望届时用户已完成.显然，这不是不是的方法.

My current approach is to call a await Task.Delay(); after a change, hoping the user is done by then. This obviously is not the way to go.

所以我的问题是:事件触发后如何重置Task.Delay()?

So my question: How to reset a Task.Delay() after a event fired?

推荐答案

您不能重置" Task.Delay ，但是您可以重置计时器，这使其成为解决问题的理想之选这个问题.

You can't "reset" a Task.Delay, but you can reset a timer which makes it an ideal candidate to solve this problem.

这是一个例子:

    private System.Threading.Timer timer;

    public void Start()
    {
        timer = new System.Threading.Timer(_ => fireMyCode());
        restartTimer();
    }

    private void onFileChanged(object sender, EventArgs e)
    {
        restartTimer();
    }

    private void restartTimer()
    {
        timer.Change(TimeSpan.FromMinutes(5), TimeSpan.FromMinutes(5));
    }

但是您不必使用计时器，您仍然可以将 Task.Delay 与其他任务一起使用:这个想法是等待两个任务，即延迟和等待文件更改(您可以使用 TaskCompletionSource 从事件中创建"任务).如果延迟任务首先完成，请触发您的代码.

But you don't have to use timers, you can still use Task.Delay with an additional task: the idea is to wait on two tasks, the delay and waiting for the files to change (you can use TaskCompletionSource to "create" a task from an event). If the delay task completes first, fire your code.

这是一个例子:

    TaskCompletionSource<object> fileChanged = new TaskCompletionSource<object>();

    private void onFileChanged(object sender, EventArgs e)
    {
        fileChanged.TrySetResult(null);
    }

    private async Task endlessLoop()
    {
        while (true)
        {
            await handleFilesNotChanged();
        }
    }

    private async Task handleFilesNotChanged()
    {
        Task timeout = Task.Delay(TimeSpan.FromMinutes(5));
        Task waitForFile = fileChanged.Task;

        if (await Task.WhenAny(timeout, waitForFile) == timeout)
        {
            fireMyCode();
        }
        fileChanged = new TaskCompletionSource<object>();
    }

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