use threads;
use threads::shared;

my %thread_state:shared;

# ignore the creation of threads

# a loop that collects all threads
while (1) {
  foreach (threads->list()) {
    if ($thread_state{$_->tid} eq 'finished') {$_->join;}
  }
  sleep 1;
  last if (&all_finished);
}

# the thread body looks like this
sub thread_body{
  # do something
  # when finished, mark itself
  {
    lock %thread_state;
    $thread_state{$threads->tid} = 'finished';
  }
}