c# - FileSystemWatcher 更改事件(对于 "LastWrite")是不可靠的

Question

我正在尝试在磁盘上的文件更新时收到通知。我有兴趣在刷新发生后立即收到此通知，但是，似乎 FileSystemWatcher 只会在流打开或关闭时发送事件。

在下面的代码中，我正在写入文件并重复将缓冲区刷新到磁盘。然而，FileSystemWatcher 只在写入开始和结束时通知我一次。

还有其他方法可以获取这些通知吗？或者我应该为此使用轮询？

代码:

class Program
{
    static void Main(string[] args)
    {
        FileSystemWatcher watcher = new FileSystemWatcher(Environment.CurrentDirectory, "Test.txt");
        watcher.Changed += watcher_Changed;
        watcher.EnableRaisingEvents = true;

        using(TextWriter writer = new StreamWriter("Test.txt"))
        {
            WriteData(writer);
            WriteData(writer);
            WriteData(writer);
            WriteData(writer);
        }

        Thread.Sleep(10000);
    }

    private static void WriteData(TextWriter writer)
    {
        writer.WriteLine("Hello!");
        writer.Flush();
        Console.WriteLine(DateTime.Now.ToString("T") + "] Wrote data");
        Thread.Sleep(3000);
    }

    static void watcher_Changed(object sender, FileSystemEventArgs e)
    {
        Console.WriteLine(DateTime.Now.ToString("T") + "] Watcher changed!");
    }
}

更新 1

我已更正 DateTime 的 ToString 函数以显示秒数。这是上面代码的输出:

11:37:47 AM] Watcher changed!
11:37:47 AM] Wrote data
11:37:50 AM] Wrote data
11:37:53 AM] Wrote data
11:37:56 AM] Wrote data
11:37:59 AM] Watcher changed!

谢谢!

Answer 1

它与 FileSystemWatcher 无关。观察者对文件系统的 LastWrite 属性的更新作出 react 。

例如NTFS 不会在每次写入时更新 LastWrite。该值被缓存并且仅在流关闭时或在其他一些未指定的时间写入。 This document说

Timestamps are updated at various times and for various reasons. The only guarantee about a file timestamp is that the file time is correctly reflected when the handle that makes the change is closed. [...] The NTFS file system delays updates to the last access time for a file by up to 1 hour after the last access

我假设类似的缓存适用于写入