#! perl -slw
use strict;
use threads;
use Thread::Queue;

sub worker {
    my( $Qwork, $Qback ) = @_;
    my $tid = threads->tid;
    print "Thread $tid started";
    while( defined( my $work = $Qwork->dequeue ) ) {
        print "Thread $tid processing workitem $work";
        $Qback->enqueue( $work * $tid );
        sleep 1;
    }
    $Qback->enqueue( undef );
    print "Thread $tid done";
}

our $WORKERS //= 10;
our $ITEMS   //= 30;

my $Qwork = new Thread::Queue;
my $Qback = new Thread::Queue;

my @pool = map threads->new( \&worker, $Qwork, $Qback ), 1 .. $WORKERS;

$Qwork->enqueue( 1 .. $ITEMS );
$Qwork->enqueue( (undef) x $WORKERS );

for( 1 .. $WORKERS ) {
    while( defined( my $res = $Qback->dequeue ) ) {
        print "Main retrieved result: $res";
    }
}
print "Main done";

$_->join for @pool