Parallel::ForkManager was written to do precisely this, and works very well.

  use Parallel::ForkManager;

  $pm = new Parallel::ForkManager($MAX_PROCESSES);

  foreach $data (@all_data) {
    # Forks and returns the pid for the child:
    my $pid = $pm->start and next;

    ... do some work with $data in the child process ...

    $pm->finish; # Terminates the child process
  }
[download]