#!/usr/bin/env perl -w

use strict;
use Parallel::ForkManager;

use 5.012;

my $max_procs = 5;

my @name_queue   = qw( bot403 );
my @future_names = qw( Fred Jim Lily Steve Jessica Bob Dave Christine Rico Sara );


my $pm =  new Parallel::ForkManager($max_procs);

# Track children in progress
my %working;

# Setup a callback for when a child finishes up so we can
# get it's exit code
$pm->run_on_finish(
  sub { my ($pid, $exit_code, $ident) = @_;
    print "** $ident just got out of the pool ".
      "with PID $pid and exit code: $exit_code\n";
    my $new = shift @future_names;
    # Done with this work unit.
    shift @name_queue;
    # Get future work to do (oversimplification of my real problem)
    push @name_queue, $new if $new;
    # Mark this entry as no longer in progress
    delete $working{$ident};
  }

);

$pm->run_on_start(
  sub { my ($pid,$ident)=@_;
    print "** $ident started, pid: $pid\n";
  }
);

$pm->run_on_wait(
  sub {
    print "** Have to wait for one children ...\n"
  },
  10
);

while( @name_queue || scalar keys %working ){
  
  # Screen out entries in progress so we don't duplicate work.
  my @to_process = grep { ! $working{$_} } @name_queue;

  if( !@to_process ){
   say "Waiting for children to finish to find new names";
   sleep 10;
   next;
  }

  foreach my $child (@to_process){
    $working{$child} = 1;
    $pm->start($child) and next;

    # This code is the child process
    say "This is $child";
    sleep 3+rand(5);
    $pm->finish(0); # pass an exit code to finish
  }
}

print "Waiting for Children...\n";
$pm->wait_all_children;
print "Everybody is out of the pool!\n";