use Parallel::ForkControl;

my $forker = new Parallel::ForkControl(
                 MaxKids => 5000,
                 MinKids => 5,
                 WatchLoad => 1,
                 MaxLoad => 5.50,
                 Code => \&mySub
);


foreach my $col (@collections) {
    $forker->run($col);
}
$forker->cleanup();

sub mySub {
     my $collection = shift;
     ......
     return;
}