scryer-prolog: Excessive memory usage in failure-driven loop

$ scryer-prolog --version
"v0.8.123-557-gebe143d"

$ scryer-prolog
?- use_module(library(between)).
   true.
?- [user].
q(E) :- X is 10^E, (between(1,X,_),false;true).
?- q(6).
Segmentation fault (core dumped)

The issue with this is not the segmentation violation (or the catchability thereof as in issue #16).

It is the excessive amount of memory allocated before the segv happens.

What’s going on?

P.S. I defined q/1 to check if the problem was top-level related or not. It seems it does not.

About this issue

Original URL
State: open
Created 3 years ago
Reactions: 2
Comments: 15 (8 by maintainers)

Most upvoted comments

It would help here to issue a clean resource error. In this manner one could distinguish between copystack/global heap overflows and call stack/local stack overflows.

UWN on Dec 14, 2023

$ sh -c 'ulimit -c 0; ulimit -v 100000; ./scryer-prolog -f'
?- [user].
query :-
   repeat,
   loop.

loop :-
   true,
   loop.

?- query.
   % Expected loop.

The variable isn’t needed. In this example the stack (local stack) is maybe growing but tail call optimization should have made this loop with constant memory.

notoria on Dec 14, 2023

@notoria Your example shows similarly erratic behavior. I can confirm that.

But the rest (why a true makes a difference) is quite puzzling to me…

stefan-kral on Dec 14, 2023

$ sh -c 'ulimit -c 0; ulimit -v 100000; ./scryer-prolog -f'
?- [user].
query :-
    repeat,
    loop(_).

loop(N) :-
    true,
    loop(N).

?- query.

It should be the same issue.

notoria on Dec 14, 2023

length(_,_) uses memory for the list. So it is not a good example to draw conclusions from.

UWN on Dec 14, 2023

@bakaq @UWN I cannot confirm this is fixed with the latest version.

Instead I find the following top-level query working fine:

?- (between(1,100000000,_),false;true).

But doing almost the same in an auxiliary predicate quickly runs out of memory:

?- [user].
q :- between(1,100000000,_),false;true.
?- q.

stefan-kral on Dec 14, 2023

This here works:

b(A,B,C):-between(A,B,C),false.
b(_,_,_).

qo :- b(1,100000000,_).

?- qo.
   true.

UWN on Dec 14, 2023

I can’t seem to reproduce this in the latest master. Memory usage doesn’t seem to scale with E at all, and there is no SEGV at least until E = 8 (it takes exponentially more time to increase it further, as expected).

bakaq on Dec 12, 2023