NTFS Filesystem Time

Question

I tested this on windows xp.

If I do

1. Create a file.
2. Write to the file.
3. Close the file.(Then, the file's LastWriteTime is changed)

But if I do

1. Create a file.
2. Set LastFileTime of the file.
3. Examine the time by calling GetFileTime (Then, the file's LastWriteTime is changed)
4. Sleep 20 seconds.
5. Write to the file.
6. Sleep 20 seconds.
7. Close the file.
8. Examine the time by calling GetFileTime (The process5's time is never applied. Why?)

Edit:

wstring fileName = L"D:\\testfile.txt";
HANDLE h = CreateFileW(fileName.c_str(), GENERIC_WRITE | GENERIC_READ, 
                    FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
                    0,
                    CREATE_ALWAYS,
                    0, 0);

FILETIME ft1, ft2, ft3;
if(!GetFileTime(h, &ft1, &ft2, &ft3))
{
    return;
}
std::cout << ft3.dwHighDateTime << std::endl << ft3.dwLowDateTime << std::endl;
ft1.dwLowDateTime = 1000000;

if(!SetFileTime(h, &ft1, &ft1, &ft1))
{
    return;
}

if(!GetFileTime(h, &ft1, &ft2, &ft3))
{
    return;
}
std::cout << ft3.dwHighDateTime << std::endl << ft3.dwLowDateTime << std::endl;

Sleep(5000);
TCHAR buffer[] = L"Test1234567890 Test1234567890 Test1234567890 Test1234567890 Test1234567890\r\n";
DWORD writeBytes = 0;
BOOL fOk = WriteFile(h, buffer, sizeof(buffer), &writeBytes, 0);
if(!fOk)
{
    return;
}
if(writeBytes != sizeof(buffer))
{
    return;
}

if(!GetFileTime(h, &ft1, &ft2, &ft3))
{
    return;
}
std::cout << ft3.dwHighDateTime << std::endl << ft3.dwLowDateTime << std::endl;

CloseHandle(h);

h = CreateFileW(fileName.c_str(), GENERIC_WRITE | GENERIC_READ, 
    FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
    0,
    OPEN_EXISTING,
    0, 0);
if(!GetFileTime(h, &ft1, &ft2, &ft3))
{
    return;
}
std::cout << ft3.dwHighDateTime << std::endl << ft3.dwLowDateTime << std::endl;

CloseHandle(h);
DeleteFile(fileName.c_str());

Could you explain me about this? Thanks.

Answer 1

Quoth the documentation:

The value of the LastWriteTime property is pre-cached if the current instance of the FileSystemInfo object was returned from any of the following DirectoryInfo methods:

[...]

To get the latest value, call the Refresh method.

Answer 2

Try to call FlushFileBuffers(h) after changing the time stamps or use FILE_FLAG_WRITE_THROUGH and FILE_FLAG_NO_BUFFERING flag during opening of the file. See in http://msdn.microsoft.com/en-us/library/aa363858.aspx#caching_behavior:

A write-through request via FILE_FLAG_WRITE_THROUGH also causes NTFS to flush any metadata changes, such as a time stamp update or a rename operation, that result from processing the request. For this reason, the FILE_FLAG_WRITE_THROUGH flag is often used with the FILE_FLAG_NO_BUFFERING flag as a replacement for calling the FlushFileBuffers function after each write, which can cause unnecessary performance penalties. Using these flags together avoids those penalties. For general information about the caching of files and metadata, see File Caching.