Shared memory in a DLL with Delphi 2.0

Sharing Memory Mapped Files... Check out the following code:

var

HMapping: THandle;

PMapData: Pointer;

const

MAPFILESIZE = 1000;

procedure OpenMap;

var

llInit: Boolean;

lInt: Integer;

begin

HMapping := CreateFileMapping($FFFFFFFF, nil, PAGE_READWRITE, 0, MAPFILESIZE, pchar('MY MAP NAME GOES HERE'));

// Check if already exists

llInit := (GetLastError() <> ERROR_ALREADY_EXISTS);

if (hMapping = 0) then begin

ShowMessage('Can''t Create Memory Map');

Application.Terminate;

exit;

end;

PMapData := MapViewOfFile(HMapping, FILE_MAP_ALL_ACCESS, 0, 0, 0);

if PMapData = nil then begin

CloseHandle(HMapping);

ShowMessage('Can''t View Memory Map');

Application.Terminate;

exit;

end;

if (llInit) then begin

// Init block to #0 if newly created

memset(PMapData, #0, MAPFILESIZE);

end;

procedure CloseMap;

begin

if PMapData <> nil then begin

UnMapViewOfFile(PMapData);

end;

if HMapping <> 0 then begin

CloseHandle(HMapping);

end;

Any two or more applications or DLLs may obtain pointers to the same physical block of memory this way. PMapData will point to a 1000 byte buffer in this example, this buffer being initialized to #0's the first time in. One potential problem is synchronizing access to the memory. You may accomplish this through the use of mutexes. Here's an example of that:

{ Call LockMap before writing (and reading?) to the memory mapped file. Be sure to call UnlockMap immediately when done updating. }

var

HMapMutex: THandle;

const

REQUEST_TIMEOUT = 1000;

function LockMap:Boolean;

begin

Result := true;

HMapMutex := CreateMutex(nil, false, pchar('MY MUTEX NAME GOES HERE'));

if HMixMutex = 0 then begin

ShowMessage('Can''t create map mutex');

Result := false;

end else begin

if WaitForSingleObject(HMapMutex,REQUEST_TIMEOUT) = WAIT_FAILED then begin

// timeout

ShowMessage('Can''t lock memory mapped file');

Result := false;

end;

procedure UnlockMap;

begin

ReleaseMutex(HMixMutex);

CloseHandle(HMixMutex);

end;

Please excuse my unnecessary begin..end's. I come from a Clipper background, and I prefer to see my logic blocks capped off with end's - easier to follow.