Good day bros. I am trying to learn how to use threads in Perl to apply it in a script that is doing calculations on a large graph. I know I need to limit the number of threads I spawn, so I've been reading up and have demo code working that limits the number of threads with semaphore and works as expected. 
#!/usr/bin/perl -w
use strict;
use threads;
use Thread::Semaphore;

my $sem = Thread::Semaphore->new(15); # max 15 threads
my @threads;
for my $i (0..5) {
    $sem->down;
    my $t = threads->create(\&mySubName, $i);
    push(@threads,$t);
}
foreach my $t (@threads) {
    print $t->join(),"\n";
}

sub mySubName {
    my $foo = shift(@_);
    return $foo * 10;
    # release slot:
    $sem->up;
}

[download]
However I have a question about the @threads array. Since that exists till then end of the loop, do the thread objects it contains only hold the values returned by the sub, or do they have other data that would eat a lot of memory? If so then the approach I have here won't work for processing all pairs of nodes in a 7000 node graph.

Assuming that's the case I tried this 

##!/usr/bin/perl -w
use strict;
use threads;
use threads::shared;
use Thread::Semaphore;

my $sem = Thread::Semaphore->new(15); # max 15 threads
my @results :shared = 1;
for my $i (0..5) {
    $sem->down;
    my $t = threads->create(\&mySubName, $i);
}

print join(" ",@results);

sub mySubName {
    threads->detach();
    my $foo = shift(@_);
    push (@results,$foo);
    $sem->up;
}

[download]
but the output is 1 0 1 2 3 which is not right.

Guidance appreciated.

In reply to Threading and join/termination question by cormanaz

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