On 08/03/2010 10:40 AM, Maik Wojcieszak wrote:
Hi,
I'm working on a port of a Delphi component to Lazarus. The component
wraps a dll for Network Communication
based on ASPLs Vortex Library but implementing a full set of "easy to
use" mechanisms for "daily work problems".
The dll itself is written in C++ with a C like interface. It is
multithreaded and uses callbacks for a lot of purposes.
The callback function/procedure is defined like
OK a "flattened" interface is necessary.
//#---------------------------------------------------------------------
// CALLBACK PROCEDURES
//#---------------------------------------------------------------------
procedure ExecuteCommandClb(tmlhandle : TML_COMMAND_HANDLE; pCBData :
Pointer); cdecl;
begin
//...
end;
Did you define cdecl specification both in C and in Pascal ? AFAIK, with
M$ Studio this is "__declspec(dllexport)", I don't know what the GNU
notation for this is.
You also can use STDCALL instead of cdecl on both sites. I seem to
remember the GNU C notation is __STDCALL, but this might be wrong.
No matter what I do inside this procedure if I reach the end the
assembler window is popping up in the debugger.
The Parameters seem to be correct.
pCBData is a Pointer to an object stored with the pointer to the
callback. The procedure is used as a proxy to call
the real worker method of the object.
You can't use C++ objects in Pascal. You need to flatten the interface
completely by explicitly communicating addresses of flat functions to do
a callback. This can be quite complicated :(.
tmlhandle is also a Pointer, but to an object that is implemented in
the dll.
Also pointers need to be "flat" and not point to C++ (or FPC) objects.
Of course a multithreaded DLL offers some even more advanced problems. I
would do a test with a singlethreaded DLL just to test all aspects of
the interface to your FPC project and activate the threads later.
It should be no problem if a thread in a DLL calls a callback to your
Pascal project. (We do this with Delphi and a PJ-SIP DLL.) But of course
such a callback can't do any "visual" LCL stuff (like writing to the
screen). Here you need to store the information (e.g. in a FIFO done
with a TThreadList) and use the mainthread to do the LCL based stuff.
-Michael
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