Read lines from a file non-blocking while doing non-blocking operations

rl.pl

use Mojo::Base -strict;

use Mojo::IOLoop::LineReader;
use Mojo::UserAgent;
use Mojo::IOLoop;
use Data::Dump 'pp';
use File::Temp qw(tempfile :seekable);

sub run {

    # write DATA to temp file
    my $fh = tempfile;
    print {$fh} do { local $/; <DATA> };
    $fh->seek( 0, SEEK_SET );    # rewind

    # Read lines from a file non-blocking while doing non-blocking operations
    my $r  = Mojo::IOLoop::LineReader->new($fh);
    my $ua = Mojo::UserAgent->new;
    $r->on(
        readln => sub {
            my ( $r, $url ) = @_;
            say "READ";
            chomp $url;
            $ua->get(
                $url => sub {
                    my ( $ua, $tx ) = @_;
                    say "GET";
                    pp( $tx->res->json->{release_count} );
                }
            );
        }
    );
    $r->start;
    return $r;
}

my $r = run();
Mojo::IOLoop->start;

__DATA__
https://fastapi.metacpan.org/v1/author/FERREIRA
https://fastapi.metacpan.org/v1/author/GBARR
https://fastapi.metacpan.org/v1/author/MIYAGAWA
https://fastapi.metacpan.org/v1/author/INGY
__END__


Output is below.

Why all READ callbacks happen before GET callbacks?

READ
READ
READ
READ
GET
{ "backpan-only" => 425, "cpan" => 1609, "latest" => 197 }
GET
{ "backpan-only" => 275, "cpan" => 68, "latest" => 28 }
GET
{ "backpan-only" => 85, "cpan" => 122, "latest" => 31 }
GET
{ "backpan-only" => 102, "cpan" => 1572, "latest" => 199 }