Delphi COM objects multithreading

Delphi COM objects multithreading

I've been programming for a while and regarding COM/ActiveX object, I'm
facing very strange issues, that are abviously above my knowledge. Here it
is. My software talks to COM objects using late binding. Since those COM
object talk to hardware (such as scientific camera for instance), I have
choosen to seralise all calls into a dedicated thread. this allows the
main thread to interact with the user. So I'm sending messages from the
main user thread (or any other thread) to the thread that is design to
dealing solely with activeX.
Here how it looks



procedure MythreadActiveX.execute;
begin
CoInitialize(nil);
Try
ComObject :=CreateOLEObject(COMID);
While not Terminated do
Begin
If PeekMessage(Msg,0,0,0,PM_REMOVE) then
Begin
TranslateMessage(Msg);
DispatchMessage (Msg);
end;
If (FEvent.WaitFor(TimOutMs)=wrSignaled) then // Wait for command
Begin
FEvent.ResetEvent;
Try
Case COM_Order of
Oder1:Begin
.........
end
Oder2:Begin
.........
end
end;
FEventComplete.SetEvent;
end;
end;
CoUnInitialize;
end;
This works like a charm with most COM server, but fails with other COM
DLL/Server, especially written in visual basic, where the I have noticed
with process explorer that the ActiveX code is executed into the main
thread despite what I did above ! The consequence result in - main thread
holding up - main thread memory corruption (with large array for
instance)... == my app crash
What is the cause ? is this related to ActiveX threading model ? I would
like to understand and to correct my code to cope with that (In that case,
the COM shall run in the main thread....)
Thanks (Since I spent time on this, i'm ready to provide more information
in order to understand)