Windows DLL with C++ interface

[Jan van der Vorst]

Denys Duchier wrote:

> jvdvorst at iae.nl (Jan van der Vorst) writes:
>
> > E.g. a function like the following 'hello' will print the warning in
> > the emulator-window but will not show a message box. Oz will just
> > stop responding.
>
> You have to keep in mind that Oz threads are not system threads.  The
> Oz thread support is very lightweight and implemented by the Oz
> engine.  All Oz threads are run by the Oz emulator (i.e. the main
> _system_ thread of the process).  They are scheduled fairly (when
> running pure Oz code) and preemptively.  Thus, all primitives (native
> extensions - as your example below) are invoked synchronously on the
> main system thread.
>
> > OZ_BI_define(BIhello,0,0)
> > {
> >         OZ_warning("Creating message box");
> >         MessageBox(NULL, "Hello World!", "Hello Jan!", MB_OK);
> >         return OZ_ENTAILED;
> > } OZ_BI_end
>
> Whenever this primitive is invoked, the entire system will block until
> MessageBox returns.

Yes, this is what I would have expected. But the problem is that
MessageBox does not return at all. The messagebox doesn't even show up.
MessageBox is a win32 call to the user32.dll that should show a message
with an OK-button. It is the win32 'Hello World' version, the most simple
program that exists, and yet somehow I can't get it working when called
from Oz
I have the feeling here that somehow there is something wrong with loading
a DLL from a C++ extension DLL.

By the way, I compile under cygwin on WINNT with gcc 3.2 (although 2.95
has the same behaviour).

best regards, Jan

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