"But the biggest lesson...the obvious optimisation..."

"Du sprichst ein großes Wort gelassen aus." (Johann Wolfgang von Goethe)

Very impressive and instructional. What else should i say?

Update:

There are two little things i would like to add:

My basic theme wasn't to calculate factorials using threads.

I wanted to explore multithreading and thought the best idea would be to use some "expensive" calculation for this. Like in a classic homework.

Unfortunately you provided a much better algorithm that avoids multithreading ;-)

I fear i hit a basic problem in this context.

And apropos little quirks:

I wrote:

sub process {
    my $number = shift;
    # lock %result;
    $result{ threads->tid() } =
      shared_clone( { $number => factorial($number) } );
    $semaphore->up;
}
[download]

It seems like i really need to say something like:

for my $key ( sort { $a <=> $b } keys %result ) {
    my $ref = $result{$key};
    while ( my ( $k, $v ) = each %{$ref} ) {
        say qq($k => $v);
    }
}
[download]

...to iterate over the results. From the docs:

"each HASH does not work properly on shared references embedded in shared structures"

Thanks for this advice and my best regards, Karl