#!/usr/bin/perl

# http://perlmonks.org/?node_id=1169958

use Time::HiRes 'sleep';
use strict;
use warnings;

my @fruits = 'fruit001' .. 'fruit020';

my $max = 5;
my $active = 0;

while(my $fruit = shift @fruits )
  {
  while( $active >= $max )
    {
    wait;
    $active--;
    }
  if( my $pid = fork )
    {
    $active++
    }
  elsif( defined $pid )
    {
    sleep 3 + rand 7;
    print "completed $fruit\n";
    exit;
    }
  else
    {
    die "fork failed $!";
    }
  }
1 while wait > 0;
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