文件夹重命名后,文件存在检查在UNC共享上返回不正确的值

Question

在Windows 7(或服务器)框中,我们在UNC共享上有一个文件夹(跨机器UNC,而不是 localhost).我们重命名该文件夹,然后检查新文件夹位置是否存在文件.即使它存在,File.Exists也需要将近5秒钟才能返回true.

完整的repro可以在https://github.com/davidebbo/NpmFolderRenameIssue上找到.这是核心代码:

// This file doesn't exist yet
// Note that the presence of this existence check is what triggers the bug below!!
Console.WriteLine("Exists (should be false): " + File.Exists("test/test2/myfile"));

// Create a directory, with a file in it
Directory.CreateDirectory("test/subdir/test");
File.WriteAllText("test/subdir/test/myfile", "Hello");

// Rename the directory
Directory.Move("test/subdir/test", "test/test2");

var start = DateTime.UtcNow;

// List the files at the new location. Here, our file shows up fine
foreach (var path in Directory.GetFiles("test/test2"))
{
    Console.WriteLine(path);
}

for (; ; )
{
    // Now do a simple existence test. It should also be true, but when
    // running on a (cross machine) UNC share, it takes almost 5 seconds to become true!
    if (File.Exists("test/test2/myfile")) break;

    Console.WriteLine("After {0} milliseconds, test/test2/myfile doesn't show as existing",
        (DateTime.UtcNow - start).TotalMilliseconds);
    Thread.Sleep(100);
}

Console.WriteLine("After {0} milliseconds, test/test2/myfile correctly shows as existing!",
    (DateTime.UtcNow - start).TotalMilliseconds);

因此,似乎初始存在检查会导致存在值被缓存,从而导致这种虚假​​行为.

问题:对此有何解释？什么是避免它的最佳方法？

注意:在Windows上使用npm(节点包管理器)时,最初会出现此问题.我这里的代码是repro的C#端口.有关原始Node/npm问题,请参阅https://github.com/isaacs/npm/issues/2230.目标是找到解决它的方法.

Answer 1

David,重定向器实现了一个否定的"File Not Found"缓存,它可以防止客户端使用未找到文件的请求充斥服务器.默认缓存时间为5秒,但您可以通过将此值设置为0来修改FileNotFoundCacheLifetime注册表值以控制缓存或禁用缓存.

详细信息:http://technet.microsoft.com/en-us/library/ff686200(v = WS.10).aspx