use threads;
use Thread::Semaphore;

my $semaphore = Thread::Semaphore->new(4);  # max number of proccesors to use

for $i (1..10) {
	my $thr = threads->new(\&sub1, $i);
	$thr->detach();
}
sleep 20;

sub sub1 {
	$semaphore->down(1);
	$tn = shift;
	print "thread $tn is working\n";
	$s = int(rand 4) +1;					# a long calculation
	sleep $s;
	$semaphore->up(1);
}