Handle leaking in WinAPI CreateFile?

Question

CreateFile allocates 2(!!) handles and CloseHandle closes only one handle when trying to get the low-level access to cd-rom device. OS Windows XP SP3, 5 of 7 tested computers works the same.

When trying to access hdd drive letter CreateFiles works OK and allocate only one handle.

Here is the sample code:

HANDLE m_driveHandle = CreateFileW("\\\\.\\E", GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
CloseHandle(m_driveHandle);

What is the possible reason or it's just a microsoft bug?

Upd. The drive name was'nt cut&pasted.. The right string is L"\\.\E:". Bug still persists.

Upd2. Problem solved! See the answer below from me (omega).

yes, we disable the possible wrapper software, including antivirus and nero (but not uninstalling it, hmmm...) — Svetlana
Does it happen if you repeatedly open and close the file via CreateFile, CloseHandle? — MSN
More likely a bug in your code than in Microsoft's code (although anything is possible). Please show more code so that we can look for problems on your side. — jdigital

Jason Owen Jason Owen · Accepted Answer · 2009-02-10T06:40:27

There seem to be a few bugs in your sample code. If it was in fact copy & pasted from your program, then there would have to be something else going on.

First, you're calling a Unicode function with a MBCS string: the first argument should either be prepended with L or surrounded with _T().

Second, and perhaps more importantly, "\\\\.\\E" is not a valid name. You're missing a trailing colon: for opening a volume, it needs to be of the form \\.\X:, or in your case "\\\\.\\E:".

After fixing those two bugs (the first preventing compilation, the second required to get anything other than INVALID_HANDLE_VALUE back), everything seemed to be working as expected. I used GetProcessHandleCount to count the number of open handles, and it was the same before and after:

HANDLE m_driveHandle = NULL;
HANDLE m_process = GetCurrentProcess();
DWORD handleCount;
GetProcessHandleCount(m_process, &handleCount);
cout << "Currently held handles: " << handleCount << endl;

for (int i = 0; i < 10; ++i)    {
    m_driveHandle = CreateFileW(L"\\\\.\\E:",
        GENERIC_READ | GENERIC_WRITE,
        FILE_SHARE_READ | FILE_SHARE_WRITE,
        NULL,
        OPEN_EXISTING,
        FILE_ATTRIBUTE_NORMAL,
        NULL
    );
    if (INVALID_HANDLE_VALUE == m_driveHandle)  {
        cout << "Invalid handle" << endl;
    }   else    {
        CloseHandle(m_driveHandle);
    }

    GetProcessHandleCount(m_process, &handleCount);
    cout << "Currently held handles: " << handleCount << endl;
}

Commenting out the CloseHandle call causes handleCount to increment as expected, as well.

Handle leaking in WinAPI CreateFile?

4 Answers