$fetch->() for 1 .. 2;
# or
$fetch->() for 1 .. 3;
# or
$fetch->() for 1 .. 4;
# or
$fetch->();
$fetch->();

##</code><code>##

$fetch->() for 1 .. 1;
# or
$fetch->();

##</code><code>##

  ### my $end = $delay->begin;
  ...
    ### $end->();

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;
use feature 'say';

use Mojo::UserAgent;
use Mojo::IOLoop;

say "PID: $$";

my @urls = (
  'mojolicious.org/perldoc/Mojo/DOM',  'mojolicious.org/perldoc/Mojo',
  'mojolicious.org/perldoc/Mojo/File', 'mojolicious.org/perldoc/Mojo/URL',
  'mojolicious.org/perldoc/Mojo/DOM',  'mojolicious.org/perldoc/Mojo',
  'mojolicious.org/perldoc/Mojo/File', 'mojolicious.org/perldoc/Mojo/URL',
);

# User agent with a custom name, following up to 5 redirects
my $ua = Mojo::UserAgent->new(max_redirects => 5);
$ua->transactor->name('MyParallelCrawler 1.0');

# Use a delay to keep the event loop running until we are done
my $delay = Mojo::IOLoop->delay;
my $fetch;
$fetch = sub {

  my ($fetch_id) = @_;
  say "FETCH ID: $fetch_id";
  say "PID: $$; URL count: ", 0+@urls, "; URLS: @urls";
  # Stop if there are no more URLs
  #return unless my $url = shift @urls;
  return unless @urls;
  my $url = shift @urls;

  say "URL (pre delay): $url";

  # Fetch the next title
  ### my $end = $delay->begin;
  say "URL (post delay): $url";
  $ua->get($url => sub {
    my ($ua, $tx) = @_;
    say "\$ua->get(): \$ua[$ua] \$tx[$tx]";
    say "$url: ", $tx->result->dom->at('title')->text;
    ### $end->();

    # Next request
    $fetch->("INNER-$fetch_id");
  });
  say "AFTER \$ua->get()";
};

# Process two requests at a time
$fetch->($_) for 1 .. 1;
#$fetch->(1);
#$fetch->(2);
$delay->wait;