result_forkmanager.txt

0.000874996185302734	1
0.00116109848022461	2
0.00148200988769531	3
0.0019071102142334	4
1.00795602798462	5
1.0085711479187	6
1.00913310050964	7
1.0098090171814	8
2.01733994483948	9
2.01780605316162	10

result_raw_fork.txt

1.00159978866577	5
1.0016028881073	3
1.00160098075867	1
1.00160384178162	4
1.00160098075867	2
2.00454998016357	9
2.00453996658325	8
2.00453901290894	7
2.00454688072205	10
2.00453901290894	6

test_forkmanager.pl

#!/usr/bin/env perl

use v5.18;
use Time::HiRes 'time';
use Parallel::ForkManager;

  my $pm = new Parallel::ForkManager(4); 
  my @links = 1..10;
  my $btime = time;
  foreach my $link (@links) {
    $pm->start and next; # do the fork
    say ((time-$btime),"\t",$link);
    $pm->finish; # do the exit in the child process
  }
  $pm->wait_all_children;

test_raw_fork.pl

#!/usr/bin/env perl

use v5.18;
use Time::HiRes 'time';


my @links = 1..10;
my $btime = time;
my $nfork = 0;
foreach my $link (@links) {
   my $pid = fork();
   die if not defined $pid;
   if ( $pid ){
     $nfork++;
     if ($nfork > 4){
       wait;
       $nfork--;
     }
   }else{
    sleep 1;
    say ((time-$btime),"\t",$link);
    exit;
   }
}