Here's the pattern I used for that on a recent project -- it's a bit more robust than yours.

use POSIX ":sys_wait_h";

my @tasks = (1..398);

my %kids;

{
  while (@tasks and keys %kids < 5) {
    $kids{fork_a_task(shift @tasks)} = "active";
  }
  {
    my $pid = waitpid(-1, 0);
    if ($pid == -1) {
      %kids = ();
    } else {
      delete $kids{$pid};
    }
  }
  redo if @tasks or %kids;
}

sub fork_a_task {
  my $i = shift;
  my $pid = fork;
  return $pid if $pid;
  unless (defined $pid) {
    warn "cannot fork: $!";
    return 0;
  }
  ## do stuff for task $i goes here...
  exit 0;
}
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-- Randal L. Schwartz, Perl hacker
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