C++/Win32: How to wait for a pending delete to complete?

Question

Please:
There are no leaked handles [1]. The file is not open by anything in our software (it could be held open by an AntiVirus or a system indexing service, etc.) The code below can be compiled and run on your computer at home/office: you can see instantly that this loop fails and by itself NEVER attempts the Delete until after ALL handles are successfully closed, and it NEVER attempts the Create until after the file is DeleteFile'd.

The Problem:
Our software is in large part an interpreter engine for a proprietary scripting language. That scripting language has the ability to create a file, process it, and then delete the file. These are all separate operations, and no file handles are kept open in between these operations. (i.e. during the file create a handle is created, used for writing, then closed. During the file processing portion, a separate file handle opens the file, reads from it, and is closed at EOF. and Finally, delete uses ::DeleteFile which only has use of a filename, not a file handle at all).

Recently we've come to realize that a particular macro (script) fails sometimes to be able to create the file at some random subsequent time (i.e. it succeeds during the first hundred iterations of "create, process, delete", but when it comes back to creating it a hundred and first time, Windows replies "Access Denied").

Looking deeper into the issue, I have written a very simple program that loops over something like this:

while (true) {
  HANDLE hFile = CreateFileA(pszFilename, FILE_ALL_ACCESS, FILE_SHARE_READ, NULL, CREATE_NEW, FILE_ATTRIBUTE_NORMAL, NULL);
  if (hFile == INVALID_HANDLE_VALUE)
      return OpenFailed;
  const DWORD dwWrite = strlen(pszFilename);
  DWORD dwWritten;
  if (!WriteFile(hFile, pszFilename, dwWrite, &dwWritten, NULL) || dwWritten != dwWrite)
      return WriteFailed;
  if (!CloseHandle(hFile))
      return CloseFailed;
  if (!DeleteFileA(pszFilename))
      return DeleteFailed;
}

As you can see, this is direct to the Win32 API, and pretty darn simple. I create a file, write to it, close the handle, delete it, rinse, repeat...

But somewhere along the line, I'll get an Access Denied (5) error during the CreateFile() call. Looking at sysinternal's ProcessMonitor, I can see that the underlying issue is that there is a pending delete on the file while I'm trying to create it again.

Questions:
* Is there a way to wait for the delete to complete?
* Is there a way to detect that a file is pending deletion?

We have tried the first option, by simply WaitForSingleObject() on the HFILE. But the HFILE is always closed before the WaitForSingleObject executes, and so WaitForSingleObject always returns WAIT_FAILED. Clearly, trying to wait for the closed handle doesn't work.

I could wait on a change notification for the folder that the file exists in. However, that seems like an extremely overhead-intensive kludge to what is a problem only occasionally (to whit: in my tests on my Win7 x64 E6600 PC it typically fails on iteration 12000+ -- on other machines, it can happen as soon as iteration 7 or 15 or 56 or never).

I have been unable to discern any CreateFile() arguments that would explicitly allow for this ether. No matter what arguments CreateFile has, it really is not okay with opening a file for any access when the file is pending deletion. And since I can see this behavior on both an XP box and on an x64 Win7 box, I am quite certain that this is core NTFS behavior "as intended" by Microsoft. So I need a solution that allows the OS to complete the delete before I attempt to proceed, preferably w/o tying up CPU cycles needlessly, and without the extreme overhead of watching the folder that this file is in (if possible).

Thanks for taking the time to read this and post a response. Clarifying Questions welcome!

[1] Yes, this loop returns on a failure to write or a failure to close which leaks, but since this is a simple console test app, the app itself exits, and Windows guarantees that all handles are closed by the OS when a process completes. So no leaks exist here.

EDIT: Solution (@sbi)

bool DeleteFileNowA(const char * pszFilename)
{
    // determine the path in which to store the temp filename
    char szPath[MAX_PATH];
    strcpy(szPath, pszFilename);
    PathRemoveFileSpecA(szPath);

    // generate a guaranteed to be unique temporary filename to house the pending delete
    char szTempName[MAX_PATH];
    if (!GetTempFileNameA(szPath, ".xX", 0, szTempName))
        return false;

    // move the real file to the dummy filename
    if (!MoveFileExA(pszFilename, szTempName, MOVEFILE_REPLACE_EXISTING))
        return false;

    // queue the deletion (the OS will delete it when all handles (ours or other processes) close)
    if (!DeleteFileA(szTempName))
        return false;

    return true;
}

Answer 1

There are other processes in Windows that want a piece of that file. The search indexer is an obvious candidate. Or a virus scanner. They'll open the file for full sharing, including FILE_SHARE_DELETE, so that other processes aren't heavily affected by them opening the file.

That usually works out well, unless you create/write/delete at a high rate. The delete will succeed but the file cannot disappear from the file system until the last handle to it got closed. The handle held by, say, the search indexer. Any program that tries to open that pending-delete file will be slapped by error 5.

This is otherwise a generic problem on a multitasking operating system, you cannot know what other process might want to mess with your files. Your usage pattern seems unusual, review that first. A workaround would be to catch the error, sleep and try again.

Answer 2

I think this is just by poor design in the file system. I have seen same problem when I worked with communication ports, opening/closing them.

Unfortunately I think the most simple solution would be to just retry to create the file a number of times if you get an INVALID_HANDLE_VALUE. GetLastError() might also give you a better way of detecting this particular INVALID_HANDLE_VALUE.

I would have preferred overlapped I/O, but there CloseHandle() and DeleteFile() don't handle overlapped operations :(

Answer 3

Silly suggestion - since it fails so infrequently, how about simply waiting some milliseconds on failure and trying again? Or, if latency is important, switch to another file name, leaving the old file to be deleted later.

Answer 4

Since you're creating a new file, processing it, then deleting it, it sounds like you don't really care about what the file name is. If that's truly the case, you should consider always creating a temporary file. That way, each time through the process, you don't have to care that the file didn't yet get deleted.

Answer 5

• Is there a way to detect that a file is pending deletion?

Use GetFileInformationByHandleEx function with FILE_STANDARD_INFO structure.

But the function can't solve your problem. @sbi's solution either.