Cannot interrupt program with system/1 about alsprolog HOT 1 OPEN

Consider:
r :- system('sleep 1'), r.
w :- system('sleep 1'), c(0, 10000000), w.
c(N, N).
c(K, N) :- write(K),nl,J is K+1, c(J, N).
Now:
?-w. can be interrupted (always during c/2).
On the one hand, I would not expect to be able to interrupt system/1 from inside prolog (or any other language??). And the reason we can't interrupt r/1 is that our computers are too fast: we can't squeeze the ^C between the system/1 call and the recursive call to r/0. I believe the ^C is always arriving during the system call, and hence being shrugged off.
Now one might argue that the ^C arriving during the system call should /NOT/ be shrugged off, but should become effective when the system call returns. Presumably in sig.c: signal_handler for the sigint case ??

from alsprolog.