"Using '/tmp' as the temp directory is badly broken"

Thank you very much for the hint.

"...What's wrong with for my n (@numbers)..."

Nothing is wrong with it. But the iterator was significantly faster in the example in my OP.

Update: Please see also this bug

Update 2:

"...iterator was ... faster"

I thought this might be of interest:

karls-mac-mini:monks karl$ ./forker.pl
numbers: 2000
processes: 4
fork: 31.1171970367432
for: 40.2419550418854
[download]

I used this code...

while(defined( my $number = $iterator->())) {
    $pm->start($number) and next;
    my $factorial = Math::BigInt->bfac($number);
    $pm->finish( 0, \$factorial );
}
$pm->wait_all_children;
[download]

...vs. this:

for my $number (@numbers) {
    $pm->start($number) and next;
    my $factorial = Math::BigInt->bfac($number);
    $pm->finish( 0, \$factorial );
}
$pm->wait_all_children;
[download]

Best regards, Karl