#!/usr/bin/perl

# https://perlmonks.org/?node_id=1228560

use strict;
use warnings;
use Time::HiRes qw( sleep );

my $maxforks = 5; # at any one time
my $active = 0;
for my $param ( 'A' .. 'M' )
  {
  $active -= wait > 0 while $active >= $maxforks;
  if( my $pid = fork )
    {
    $active++;
    print "active forks: $active\n";
    }
  else
    {
    create_file($param);
    defined $pid and exit;
    }
  }
$active -= wait > 0 while $active;

sub create_file
  {
  sleep 0.001 + rand 1;
  my $parameter = shift;
  warn "pid $$ create_file('$parameter')\n";
  # do somethng
  }