CreateFileMapping fails with hFile other than INVALID_HANDLE_VALUE - delphi

Question

update - solved and answered, offending lines have been commented out
Brief description
I am having a problem linking CreateFile with CreateFileMapping even though I use (GENERIC_WRITE or GENERIC_WRITE) for CreateFile, with PAGE_READWRITE for CreateFileMapping
Detailed description
I am using CreateFileMapping to share memory between proceses.
the actual mechanics of that is working fine, assuming I don't map to a physical file and instead use INVALID_HANDLE_VALUE for the first parameter to CreateFileMapping. This is fine, however what I'd like to achieve is for the main process that creates this map to use a disk based file, and flush it to the drive, periodically, and when it shuts down, so the data is automatically saved.
Code follows...
(when i run this, i get "Error 5 : Access is Denied" as the ShowMessage)
const MaximumMapSize = 256 * 1024;
var virtualMemoryPath : string = '';
function getFileHandle(mapname : string; maxSize : dword) :THandle;
var diskfilename : string;
lpFileName: PChar;
dwDesiredAccess: DWORD;
dwShareMode: DWORD;
lpSecurityAttributes: PSecurityAttributes;
dwCreationDisposition : dword;
dwFlagsAndAttributes: DWORD;
hTemplateFile : THandle ;
temp : pointer;
begin
Result := INVALID_HANDLE_VALUE;
if (maxSize <= MaximumMapSize) and (Length(virtualMemoryPath) > 0) then
begin
diskfilename := virtualMemoryPath+mapname+'.bin';
if FileExists(diskfilename) then
Sysutils.DeleteFile(diskfilename);
lpFileName := PChar(diskfilename);
//dwDesiredAccess := GENERIC_WRITE or GENERIC_WRITE;//<<<wrong
dwDesiredAccess := GENERIC_READ or GENERIC_WRITE;
dwShareMode := 0;//FILE_SHARE_READ or FILE_SHARE_WRITE;//<<wrong
lpSecurityAttributes := nil;
dwCreationDisposition := CREATE_ALWAYS;
dwFlagsAndAttributes := 0;
hTemplateFile := 0 ;
Result := CreateFile(
lpFileName,
dwDesiredAccess,
dwShareMode,
lpSecurityAttributes,
dwCreationDisposition,
dwFlagsAndAttributes,
hTemplateFile);
if (Result <> INVALID_HANDLE_VALUE) then
begin
GetMem(temp,maxsize);
ZeroMemory(temp,maxsize);
FileWrite(result,temp^,maxSize);
FreeMem (temp,maxsize);
FlushFileBuffers(result);
SetFilePointer(result,0,0,FILE_BEGIN);
end;
end;
end;
function createMap (mapname : string ; maxSize: dword; var hFile: THandle) : THandle;
var
lpFileMappingAttributes: PSecurityAttributes;
flProtect : DWORD;
dwMaximumSizeHigh : DWORD;
dwMaximumSizeLow : DWORD;
lpName : PChar;
LastError : dword;
begin
Result := INVALID_HANDLE_VALUE;
if (maxSize > MaximumMapSize) then
exit;
// create a disk the file or return INVALID_HANDLE_VALUE if settings have not defined a path to folder
hFile := getFileHandle(mapname,maxSize);
lpFileMappingAttributes := nil;
flProtect := PAGE_READWRITE;
dwMaximumSizeHigh := 0;
dwMaximumSizeLow := maxSize;
lpName := PChar(mapname);
Result := CreateFileMapping(
hfile,
lpFileMappingAttributes,
flProtect,
dwMaximumSizeHigh,
dwMaximumSizeLow,
lpName);
if (Result = 0) then
begin
if (not (hFile = INVALID_HANDLE_VALUE) ) then
CloseHandle(hFile);
hFile := 0;
LastError := GetLastError();
ShowMessage( Format('Error %d : %s',[LastError,SysErrorMessage(LastError)]) );
end
else
begin
ShowMessage(Format('Returing handle %d',[result]));
if (hFile = INVALID_HANDLE_VALUE) then
hFile := 0;
end;
end;

Answer 1

dwDesiredAccess := GENERIC_WRITE or GENERIC_WRITE;
dwShareMode := FILE_SHARE_READ or FILE_SHARE_WRITE;
This cannot work. You'll need read and write access. Also, creating a view requires the operating system to be sure that it is the only one that can write to the file. There's no mechanism to detect another process writing to the file, other than through a view, and ensure that such a write is visible in memory in a timely and synchronous manner. Particularly the synchronous update is impossible to implement with multiple threads accessing the view.
Read sharing is similarly unwise, the operating system provides no guarantee at which time it updates the file from the view. The only guarantee is that it will be updated when all views are closed. Which also means that an orderly shutdown of Windows is required, you cannot make this reliable against mishaps like a power loss. Again, reads need to be done through the view, not the file. The only appropriate choice is no sharing.

Answer 2

The mistake is here:
GENERIC_WRITE or GENERIC_WRITE
You meant:
GENERIC_READ or GENERIC_WRITE
Fix that and your file mapping can be created.
I agree with Hans that you should not be sharing the file handle.