Hi,
I am trying to use multithreaded dll for network communication in lazarus. I've ported a component
from Delphi which works fine there and get a crashing app with lazarus.
I've tracked down the problem to a callback function which is called by a thread from the dll.
I don't have any clue how to solve this problem at the moment and need help.
I've provided a demo project together with a dll to reproduce the problem.
My Versions (again)
Lazarus IDE v0.9.28.2 Beta
MS Windows XP Prof DE sp3
FPC Version 2.2.4
What I basically do is passing a pointer to a calback funtion to a dll
writte in c++ (Visual Studio 2005) and call it from there.
** The follwing code is from the example attached to this mail **
procedure OnExecuteClb(pCBData : Pointer); cdecl;
begin
...
end;
The function is passed to the dll like this
...
FHandle := uVCMTDLL.vcmtdll_NewThread();
uVCMTDLL.vcmtdll_RegisterCallback(FHandle,@OnExecuteClb,self);
...
The test includes a dll which has the following interface
...
#define VCMTDLL_API __declspec(dllexport)
namespace VCMTDLL {
typedef void* MT_THREAD_HANDLE;
extern "C" {
VCMTDLL_API MT_THREAD_HANDLE vcmtdll_NewThread(); // create a new
thread object
VCMTDLL_API void vcmtdll_DeleteThread(MT_THREAD_HANDLE ahandle); //
delete an existing thread object
VCMTDLL_API void vcmtdll_RegisterCallback(MT_THREAD_HANDLE ahandle,
void* pCBFunc, void* pCBData); // pass a callback to execute inside the
thread context
VCMTDLL_API void vcmtdll_StartThread(MT_THREAD_HANDLE ahandle, unsigned
int iDelay); // start the execution with a delay of <iDelay> milliseconds
}// extern "C"
...
with a loop in the callback function everything is fine
...
x := 0;
while x < 100 do
begin
x := x + 1;
end;
...
I can execute it without problems.
BUT if I create and destroy an object inside the procedure the app
crahes or hangs after several runs of the test (between 1 an 10 starts).
the object:
...
TVCMTDummyObject = class
private
public
Tag : Integer;
end;
...
the code in the callback
...
a := TVCMTDummyObject.Create;
a.Free;
...
Another problem is that a PostMessage from the callback's thread context
immediatly crashes the app. But this may be resolved later.
If there is anybody who uses a similar mechanism in his lazarus project
and knows how to solve this problem it'd be great.
The demo project together with dll is attached too.
Best Regards
Connor