use strict;
use warnings;

use HTTP::Async;
use HTTP::Request;

my $url = ...;
my $async = HTTP::Async->new;

$async->add(HTTP::Request->new(GET => $url));

while ( $async->not_empty ) {
    if ( my $response = $async->next_response ) {
        # we have a reply from server or timeout
        # deal with $response
    } else {
        # still waiting for a response from server,
        # so do something else
    }
}