Asynchronous ReadDirectoryChangesW fails with ERROR_INVALID_PARAMETER - winapi

Question

I've managed to use ReadDirectoryChangesW synchronously, but when I attempt to use completion ports, ReadDirectoryChangesW always returns ERROR_INVALID_PARAMETER. I guess there should be some obvious error in my code, but I cannot figure it.
My code is based on How to use ReadDirectoryChangesW() method with completion routine?
const wchar_t *directory = L"X:\\X";
HANDLE h = CreateFile(
directory,
FILE_LIST_DIRECTORY,
FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
NULL, OPEN_EXISTING,
FILE_FLAG_BACKUP_SEMANTICS|FILE_FLAG_OVERLAPPED, NULL);
if (h==INVALID_HANDLE_VALUE) return;
HANDLE p = CreateIoCompletionPort(h,0,0,1);
if (p==NULL) {CloseHandle(h); return;}
DWORD *buffer =new DWORD[4096];
DWORD bytesReturned;
DWORD notifyFilter = FILE_NOTIFY_CHANGE_FILE_NAME
| FILE_NOTIFY_CHANGE_DIR_NAME
| FILE_NOTIFY_CHANGE_SIZE
| FILE_NOTIFY_CHANGE_LAST_WRITE;
while (true) {
OVERLAPPED overlapped;
memset(&overlapped,0,sizeof(overlapped));
BOOL success = ReadDirectoryChangesW(h,
&buffer[0],
4096*sizeof(DWORD),
FALSE, notifyFilter,
NULL, //&bytesReturned,
&overlapped,myFileIOCompletionRoutine);
if (!success) {
//always ERROR_INVALID_PARAMETER
CloseHandle(h);
CloseHandle(p);
return;
}
}

Answer 1

As Hans Passant kindly reminds, the documentation already says that a completion routine must not be used if the directory is associated to a completion port. In this case I solved the problem by waiting on the completion port, i.e. ReadDirectoryChangesW(...,&overlapped,0);
Complete code is below.
while (true) {
OVERLAPPED overlapped;
memset(&overlapped,0,sizeof(overlapped));
BOOL success = ReadDirectoryChangesW(h,
&buffer[0],
4096*sizeof(DWORD),
FALSE, notifyFilter, 0, &overlapped,0);
if (!success) {
if (GetLastError()==ERROR_INVALID_HANDLE) {
//asynchronously closed by cancel
CloseHandle(p); //close completion port
return 0;
} else {
CloseHandle(h); //close directory handle
CloseHandle(p); //close completion port
return 1;
}
}
DWORD di;
LPOVERLAPPED lpOverlapped;
if (!GetQueuedCompletionStatus(p,&bytesReturned,&di,&lpOverlapped,1000)) {
int ret;
if (GetLastError()==WAIT_TIMEOUT) {
if (GetFileAttributes(directory)!=INVALID_FILE_ATTRIBUTES) {
continue; //timeout
} else {
//directory has been deleted or renamed
ret=0;
}
} else {
//other failure
ret=1;
}
CloseHandle(h); //close directory handle
CloseHandle(p); //close completion port
return ret;
}
char* ptr = (char*)&buffer[0];
char* end = ptr+bytesReturned;
while (ptr<end) {
FILE_NOTIFY_INFORMATION *info = (FILE_NOTIFY_INFORMATION*) ptr;
//process FILE_NOTIFY_INFORMATION
ptr+=info->NextEntryOffset;
if (!info->NextEntryOffset) break;
}
}