#!/usr/bin/perl

# https://perlmonks.org/?node_id=1217948

use strict;
use warnings;
use Data::Dump 'dd';
use Storable qw( freeze thaw );
use Time::HiRes qw( time sleep );
use IO::Select;

my $maxforks = 20;
my @ids = 'job01' .. 'job38'; # it is cool that this works
my $sel = IO::Select->new;
my $start = time;
my @answers;

while( @ids or $sel->count ) # unstarted or active
  {
  while( @ids and $sel->count < $maxforks ) # start all forks allowed
    {
    my $id = shift @ids;
    if( open my $fh, '-|' ) # forking open
      {
      $sel->add( $fh ); # parent
      }
    else # child code goes here
      {
      sleep rand;
      print freeze { id => $id, pid => $$, time => time - $start };
      exit;
      }
    }
  for my $fh ( $sel->can_read ) # collecting child data
    {
    local $/;
    push @answers, thaw <$fh>;
    $sel->remove( $fh );
    }
  }

dd \@answers;