[fpc-pascal] Delphi ShareMem -DLL-pchar

[Matt Emson]

> Can anyone comment on the Delphi unit "ShareMem" and if FPC ever did any 
> work to incorporate what this Delphi unit is doing for DLL shared memory 
> managment?  I'm looking so far, at the docs on creating a memory manager, 
> and at the strings unit, which has some pchar utilities in it.

I don't use it any more. I use FastMM or BucketMM.

you only really need SHareMem if you are passing String types 
(string/AnsiString etc) to a DLL. It doesn't sound like you're doing that.

Beware, Sharemem is slow and buggy in my experience. Also, you would need 
sharemem in FPC as Delphi assumes you are sending your Delphi types 
(strings, classes etc), that dictate you need Sharemem, to another Delphi 
process.


> This article, http://delphi.about.com/od/objectpascalide/l/aa103003a.htm 
> explains much about the Delphi related, Win32 DLL pointer and shared 
> memory problems.  I'm working on creating a DLL between two Win32 
> applications, but having a lot of exception and pointer related problems 
> to do with pchar and asciiz data transfer.

the only way to avoid issues is to make sure the process that allocates the 
buffer deallocates it. That fixes most issues. C gets round it because you 
generally use the same compiler and Malloc etc. With Delphi and FPC, you are 
going to have issues because they are two completely different compilers.

I'd do something like:

function getFpcStrBuffer(buffer: pchar; const size: integer): boolean;

and

procedure freeFpcStrBuffer(buffer: pchar); //maybe size too?

then

var
  b: pchar;
begin
  if getFpcStrBuffer(b, 21) then
  try

     callAFpcDllRoutine(b, 21);

  finally
    freeFpcStrBuffer(b);
  end;

Do that in the DLL yhou want to pass data TO. So FPC would implement it, for 
example. Get the Delphi code to then allocate and free buffers using that 
routine. Something ike that.

Avoid using STRING/ANSISTRING/WIDESTRING when passing to a DLL like the 
plague.

Sorry lack of sleep.. must go to bed. Hopefully that makes sense.

M