Perl OOP 4

#!/usr/bin/env perl

use v5.14;
use strict;
use warnings;
use Data::Dumper;

my $wbuf1=3;
my $wbuf2=3;
my $first;

my $wtr1;
my $wtr2;
print "start\n";

$first = sub {
    my $done_f = shift;
    $wtr1 = sub {
        print "start wtr1\n";
    my $done_1 = shift;
    my $mbuf=$wbuf1;
    print "cb $wbuf1 $mbuf\n";
    $wbuf1--;
    if ( $wbuf1 ) {
            print "cb wbuf1\n";
            $wtr1->($done_1);
    } else {
            print "cb undef\n";
            undef $wtr1;
            $done_1->();
            print "after exit\n";
    }
    print "return wtr1\n";
    print "cb $wbuf1 $mbuf\n";
    };
    $wtr2 = sub {
    print "start wtr2\n";
    my $done_2 = shift;
    my $mbuf=$wbuf2;
    print "cb $wbuf2 $mbuf\n";
    $wbuf2--;
    if ( $wbuf2 ) {
            print "cb wbuf2\n";
            $wtr2->($done_2);
    } else {
            print "cb undef\n";
            undef $wtr2;
            $wtr1->($done_2);
            print "after exit\n";
    }
    print "return wtr2\n";
    print "cb $wbuf2 $mbuf\n";
    };
    $wtr2->( # Start !!!
    sub {
        my $done_cb = shift;
        print "exit $wbuf1 $wbuf2\n";
    }
    );
};
$first->();
print "stop\n";