Sharing Memory Mapped Files... Check out the following code:
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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;
end;
procedure CloseMap;
begin
if PMapData <> nil then begin
UnMapViewOfFile(PMapData);
end;
if HMapping <> 0 then begin
CloseHandle(HMapping);
end;
end;
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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:
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{ 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;
end;
end;
procedure UnlockMap;
begin
ReleaseMutex(HMixMutex);
CloseHandle(HMixMutex);
end;