----- Original Message -----
From: "Matt Emson" <[EMAIL PROTECTED]>
To: "afpTeam" <[EMAIL PROTECTED]>; "FPC-Pascal users discussions"
<fpc-pascal@lists.freepascal.org>
Sent: Tuesday, September 05, 2006 7:45 PM
Subject: Re: [fpc-pascal] Delphi ShareMem -DLL-pchar
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.
Good. Especially that I don't have access to the Delphi program itself,
only that it provides a DLL stub interface, but that's part of the
problem... the authors chose to use variant types as the parameters being
passed, so as I write a DLL to interface with it, I'm being force- fed large
allocation variant types, having to use largestring models and but only a
single shortstring that comes along for the ride with the variants.
Fortunately, as this is the client side, I can do a socket interface to that
half of the two apps and still survive, even remote the application if I
choose to.
The other app, which is serving data to my DLL and hense to Delphi through
my DLL, is a more modern platform and has a much more germane approach to
Win32 memory management. It has been interfaced with VB and several other
newer compiler based apps, quite succesfully. It is the one however, which
is dictating AsciiZ, but then showing examples of "String" type to be fed to
it, rather than pchars. I was successful in exchanging data to it with FPC,
even typecasting pchars to it, via an EXE, and hopefully that may fare well
in a DLL also, so long as I don't have to convert that back to Delphi
variants, but just send to Delphi, via socket. Damn, is that ugly, or
what? LOL
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.
Agreed.
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
Thanks for the suggestions. Ditto sleep. Will try some tomorrow but mostly
you're suggesting the same thing I think I've been seeing.
Thank you.
F
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