require 'resolv'
require 'resolv-replace'


def multiple_lookup(*names)
    dns = Resolv::DNS.new
    results = {}
    threads = []
    names.each do |name|
        threads << Thread.new(name) do |name|
            begin
                dns.each_address(name) { |a| (results[name] ||= []) << a }
            rescue Resolv::ResolvError
                results[name] = nil
            end
        end
    end
    threads.each { |t| t.join }
    return results
end


domains = ("a".."z").collect { |l| l + '.com' }
multiple_lookup(*domains).sort.each do |name, addresses|
    if addresses
        puts "#{name}: #{addresses.size} " + \
             "address#{addresses.size == 1 ? "" : "es"}"
    end
end