Jan Wielemaker wrote:
The only thing you are allowed to do from the GMP allocation functions is stop the process.
This is not my understanding: where did you get this restriction from?
Quoting from the GMP manual (GMP 4.2.1, SuSE RPM):
There's currently no defined way for the allocation functions to recover from an error such as out of memory, they must terminate program execution. A `longjmp' or throwing a C++ exception will have undefined results. This may change in the future.
I see. Well, I think the situation is that they do not make promises (not now) but either they will need to do so if they want a decent C++ interface. My experience is that when you get an out of memory error from GMP it is perfectly safe to discard the GMP object involved and computation can continue: we are testing this all the time and it never ever failed.
So, I wonder how you safely recover. Surely if you call Prolog, which calls a GMP function, which gets you using longjmp or a C++ exception back to the C++ program, you haven't made Prolog particulary happy. Seems from the rest that you are calling C++ from Prolog, which might make things a bit better ...
Yes, we are calling C++ from Prolog.
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. Cheers,
Roberto