use strict;
use warnings;

use Parallel::ForkManager qw( );

my @data = (
   ...
);

my @tasks = (
   sub { printf("%s\n",                 $_[0]); },
   sub { exec('/home/working/perl1.pl', $_[0]); },
   sub { exec('/home/perl2.pl',         $_[0]); },
);

{
   my $task_id;
   my @idle = (0..$#tasks);
   my %alloc;

   my $pm = Parallel::ForkManager->new(scalar(@tasks));

   $pm->run_pre_fork(sub {
      $task_id = shift(@idle);
   });

   $pm->run_on_start(sub {
      my ($pid) = @_;
      $alloc{$pid} = $task_id;
   });

   $pm->run_on_finish(sub {
      my ($pid) = @_;
      push(@idle, delete($alloc{$pid}));
   });

   foreach my $data (@data) {
      my $pid = $pm->start and next;
      $tasks[$task_id]->($data);
      $pm->finish;
   }
}

##</code><code>##

  $s->wait_children;
  if ($s->{max_proc}) {
    my $pid=fork();

##</code><code>##

  $s->wait_children;
  $s->pre_fork;
  if ($s->{max_proc}) {
    my $pid=fork();

##</code><code>##

sub run_pre_fork { my ($s,$code)=@_;
  $s->{pre_fork}=$code;
}

sub pre_fork { my ($s)=@_;
  $s->{pre_fork}->() if ref($s->{pre_fork}) eq 'CODE';
}