memory mapping

[csbrmg]

I seem have a few problems returning a reference to a shared memory location and keep on getting a run time at the specified location below...
this is the code

class function TActivityLogger.NewInstance: TObject;
var
llInit:Boolean;
temp:LoggerPointer;
begin
HMapping:=CreateFileMapping($FFFFFFFF,nil,PAGE_READWRITE,0,MAPFILESIZE,pchar('my mem'));
...
llInit:=(getLastError()<>ERROR_ALREADY_EXISTS);
if ( llInit ) then //first instance
begin
temp:=mapViewOfFile(HMapping,fILE_MAP_all_access,0,0,0);
....
Result:=temp^.instance ;
end
else
begin
HMapping:=openfilemapping( FILE_MAP_all_access,true, pchar('my mem'));
...
temp:=MapViewOfFile(HMapping,FILE_MAP_all_access,0,0,0);
...
Result:=temp^.instance;//<-Runtime error occurs here
end;
end;

 

[BillDoorNZ]

From reading the doco, I'd hazard a guess that the way you are cerating the HMapping ref is the problem:

HMapping:=CreateFileMapping($FFFFFFFF,nil,PAGE_READWRITE,0,MAPFILESIZE,pchar('my mem'));


According the the doco you need to specify the LPSECURITY_ATTRIBUTES so that you can inherit the handle later on (as you are attempting with):

HMapping:=openfilemapping( FILE_MAP_all_access,true, pchar('my mem'));


I HATE working with security attributes and almost always create them as 'anyone/everyone has access'. In you case, its not a problem as y're obviously using hte mapping file for sharing info with other processes or the like - have fun with the synchronisation .

Here is some sample code for creating nice, insecure security attributes:

var
FSecurityAttributes: TSecurityAttributes;
FSD: TSecurityDescriptor;
begin
InitializeSecurityDescriptor(@FSD, SECURITY_DESCRIPTOR_REVISION);
SetSecurityDescriptorDacl(@FSD, True, nil, False);
FSecurityAttributes.nLength := Sizeof(FSecurityAttributes);
FSecurityAttributes.lpSecurityDescriptor := @FSD;
FSecurityAttributes.bInheritHandle := True;
end;