[PPL-devel] [SWIPL] Re: GMP memory allocation problem in SWI-Prolog 5.6.38 and following versions

[Jan Wielemaker]

On Monday 08 October 2007 14:23, Roberto Bagnara wrote:
> Jan Wielemaker wrote:
> >>>>> Anyway for the others, I added
> >>>>>
> >>>>> 	PL_action(PL_GMP_SET_ALLOC_FUNCTIONS, TRUE)
> >>>>>
> >>>>> if you want Prolog's GMP allocation initialised *now* (without
> >>>>> initializing the rest of SWI-Prolog).  or
> >>>>>
> >>>>> 	PL_action(PL_GMP_SET_ALLOC_FUNCTIONS, FALSE)
> >>>>>
> >>>>> If you want to stop Prolog from setting the allocation functions. 
> >>>>> Must be called before PL_initialise(), of course.
> >>>>
> >>>> I see how to use that in the foreign-calls-Prolog case.
> >>>> How can I achieve that in the Prolog-calls-foreign case (which is the
> >>>> one I am mostly interested in)?
> >>>
> >>> You mean you load a shared object into Prolog? Good!
> >>
> >> No, I am having problems with libraries statically linked to the
> >> SWI-Prolog system.  These libraries (written in C++) use several
> >> statically allocated GMP numbers.  When the system starts, the
> >> statically allocated variables are initialized with the GMP's memory
> >> allocation function.  Then SWI-Prolog is given control and the
> >> allocation functions are changed.  Then the system exits and the
> >> statically allocated variables are destroyed with the wrong (i.e.,
> >> SWI-Prolog's) allocation function: which results into a segmentation
> >> fault.  This change you have made to SWI-Prolog is really breaking
> >> everything here.
> >
> > I'm not getting it. I think there are two situations: you embed Prolog,
> > so you call PL_initialise() and you can call the
> > PL_action(PL_GMP_SET_ALLOC_FUNCTIONS, FALSE) before it or you keep the
> > Prolog toplevel and you load your code as a .so file into Prolog. I
> > think both work fine, even with global C++ initializers. What am I
> > missing?
>
> Probably the fact that the constructors of global variables are all
> run (in unspecified order) before main() is given control.
> You can compile the following with

This is the case if you embed SWI-Prolog, but in main() you call

	PL_action(PL_GMP_SET_ALLOC_FUNCTIONS, FALSE)

and Prolog won't touch the GMP allocator anymore. If you link your code
to a shared object the global constructores are executed at the moment
you load the .so file into Prolog.  Still puzzled ...

	--- Jan