[fpc-pascal] C++ > C wrapper callback > Pascal Continues UPDATE
urbansound at sbcglobal.net
Thu Jul 28 08:06:46 CEST 2005
See bottom post
----- Original Message -----
From: "Urbansound" <urbansound at sbcglobal.net>
To: <fpc-pascal at lists.freepascal.org>
Sent: Wednesday, July 27, 2005 11:05 PM
Subject: C++ > C wrapper callback > Pascal Continues
> Reply Peter and Tomas, is below, each... Thread pruned.
>> 2. Re: C++ > C wrapper callback > Pascal Continues (Peter Vreman)
>> 3. Re: C++ > C wrapper callback > Pascal Continues (Tomas Hajny)
>> Message: 2
>> Date: Wed, 27 Jul 2005 14:26:57 +0200 (CEST)
>> It is an internal function implicitly called by the compiler.
> The s call in the message line was converted to a "pointer(s)". I found
> the FPC_INITIALIZEUNITS at Main, in the ASM output and understand now that
> the compiler handles this fully and that FPC_INITIALIZEUNITS could not be
> the issue. Perhaps this thread will help others new to FPC to know this
> too on the chance they may research it. Thank you. Present code is at
> bottom to thin down the thread.
> Tomas below, may be onto it, as a threading issue. Thanks still for your
> help. Mike
>> Well, maybe I misunderstood the original post, but my understanding was
>> that it's about a _Pascal_ program calling some C function (which is in
>> fact just a wrapper for C++, but that shouldn't matter) and passing some
>> other Pascal function as a callback. If this is the case and the callback
>> function runs within the same thread as the block calling the C wrapper,
>> Pascal units should be initialized since the main Pascal program startup,
>> shouldn't they? If a new thread is started by the C++ program, you need
>> perform (Pascal) initialization of the thread (probably on the first
>> to the callback function). Could you clarify this, please (link to the
>> complete sources or preferrably their simplified but still compilable
>> version would probably serve the best as already pointed out by Peter)?
> Thanks Tomas.
> 1) Current function is below, due to pruning the thread.
> 1) Clearly I was off course on FPC_INITIALIZEUNITS
> 2) You're understanding is correct C++api > C+wrpr > Pascal as callback
> The wrapper is actually C code in a .cpp, for functionality
> 3) The API is multi-threaded, having dl'd a thread monitor, showing as
> many as 5 threads spawened to the API and accompanied executable. As
> well, a call back occurs by default from the API, at runtime, suggesting
> it fires off a single dummy callback event.
> 4) Can you suggest an approach on the Pasacl Initialization to the thread
> and/or some of the areas I should be looking up toward doing the work?
> Google is my friend. ;-)
> Thank you again. Mike
> //------- Current function model below here
> function L1_Callback(quote : pointer) : integer; stdcall; export;
> bid_price : single = 0.0;
> s : ansistring = '';
> SendMessage(listbox, LB_ADDSTRING, 0, longint(Pchar('L1 Callback')));
> // -- either commented below will cause crash
> //SendMessage(listbox, LB_ADDSTRING, 0, longint(Get_secsym(quote)));
> //bid_price := Get_l1_BidPrice(quote);
> s := FloatToStr(bid_price);
Per Tomas suggestions:
Among our C equivelent of the Pascal program, we did the following, which
confirms that the C+ callback and Pascal, are on the same, single thread,
which was confirmed with a thread monitoring tool during operation. (See
comment at bottom).
void ShowThreadInfo(char* id)
sprintf(s,"%s Thread ID: %08X Thread Handle:
SendMessage(listbox, LB_ADDSTRING, 0, (LPARAM)s);
int _stdcall L1_Callback(void* quote)
Given that an equivelent C program, (built by modifying the Pascal program
to suit C syntax/method), runs without a problem and yet there is no evident
reason code-wise for the problem, what is the next step in resolving the
matter. I can use GDB, though I am new to it, as of this issue. If someone
is willing to give me a guide on what command/data gdb can afford us, I'd
certainly make the effort here, unless there are other suggestions? This is
fpc 2.00, so I'm current w/stable.
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