sub worker_thread
{
  while ( my $item = $processing_q -> dequeue() )
  {
     # do stuff to $item
  }
}

for ( my $count = 0; $count < $nthreads; $count++ )
{
  my $thr = threads -> create ( \&worker_thread );
}

$processing_q -> enqueue ( @server_list ); 
$processing_q -> end;

foreach my $thread ( threads -> list() )
{
  $thread -> join();
}