How to prepare for forking? #65
Description
I'm writing code to fork multiple processes, each of which will test one number - anything from a primality test to a full factorization. Other than loading MPU and MPUG, what should I do in the parent to ensure that tables of primes and the like are appropriately cached before forking? I suspect I should at least be calling prime_precalc(), but I don't know how to estimate or discover how many primes it will need to factorize numbers in a given range.
I don't see anything in MPU-0.73 or MPUG-0.52 docs about this, apologies if I've missed something.
The details: I have an array of subrefs @check that typically check is_prime($value) or is_semiprime($value). I'll essentially be replacing this fragment of my code:
return 1 if all { $_->() } @check;
with something like:
for my $check (@check) {
if (my $pid = fork) {
$waitpids{$pid} = 1;
} else {
exit $check->() ? 0 : 1;
}
}
# now look for exit codes via waitpid()
# as soon as one exits non-zero we can kill the rest
.. because while some of the checks return in under a second, others are taking hours or days. This way, my hope is that it'll run as fast as the fastest (failing) check rather than having to do them in order. The numbers under consideration will initially be in the 80-105 digit range, and I estimate that I may need to check up to 230 million sets before finding the solution I'm looking for. (If that one works, I have another batch of 140-digit numbers to check.)
I'm hoping that fork() will prove lightweight enough to make this efficient. If not, an alternative would be to fork a pool of longer-lived servers that accept a request but can be interrupted with a signal: less process churn, but much fiddlier to code to ensure no signals are lost.