Why does ReadDirectoryChangesW omit events?

Question

I use ReadDirectoryChangesW to watch a specified directory and update indexing structures whenever a change is detected. I use the following code (roughly)

var
  InfoPointer : PFileNotifyInformation;
  NextOffset : DWORD;
...
while (not Terminated) do begin
  if ReadDirectoryChangesW (FDirHandle, FBuffer, FBufferLength, True,
                            FFilter, @BytesRead, @FOverlap, nil) then
    begin
    WaitResult := WaitForMultipleObjects (2, @FEventArray, False, INFINITE);
    if (WaitResult = waitFileChange) then
      begin 
      InfoPointer := FBuffer;
      repeat
        NextOffset := InfoPointer.NextEntryOffset;
        ...
        PByte (InfoPointer) := PByte (InfoPointer) + NextOffset;
      until NextOffset = 0;
      end;
    end;
end;  

Filter is

FFilter :=  FILE_NOTIFY_CHANGE_FILE_NAME or
            FILE_NOTIFY_CHANGE_DIR_NAME or
            FILE_NOTIFY_CHANGE_SIZE or
            FILE_NOTIFY_CHANGE_LAST_WRITE;

and the directory handle is obtained like this:

FDirHandle := CreateFile (PChar (FDirectoryWatch.WatchedDirectory),
                          FILE_LIST_DIRECTORY or GENERIC_READ,
                          FILE_SHARE_READ or FILE_SHARE_WRITE or FILE_SHARE_DELETE,
                          nil, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS or   
                          FILE_FLAG_OVERLAPPED, 0);         

When I delete multiple files I get only one event and NextOffset is 0! And when I delete a directory I get only one event for the directory. What if I want one event for each file in the directory?

Any help would be appreciated.

Answer 1

We've had the same problem with losing events, especially if a lot of changes happens at the same time, ie. 500 files are copied to the monitored directory.

In the end we found Cromis and use the Directory watch. We have never looked back again.