You seem to be confused about the order of execution here:

...
                    my $return_code;
                    my $cb = sub {
                        my $ret_val =  shift;

                        $return_code = $ret_val;
                    };

                    add_route($ip_address, $next_hop, $cb);

                    print $return_code;
                    #post_job_process($return_code, $file_name);
...
[download]

add_route() will basically return immediately, and you print out $return_code immediately. What you seem to want is to print out $return_code in your callback instead.

As an alternative to printing in the callback, you might want to ->send the return code using a condvar, and ->recv that somewhere up the call stack where you actually need it.