better_async_port_scanner.rb

#!/usr/bin/env ruby

require 'async/io'
require 'async/semaphore'

def scan_port(host, port, timeout)
  Async do |task|
    task.with_timeout(timeout) do
      address = Async::IO::Address.tcp(host, port)
      Async::IO::Socket.connect(address).close
      puts "#{port} open"
    rescue Errno::ECONNREFUSED
      puts "#{port} closed"
    rescue Async::TimeoutError
      puts "#{port} timeout"
    end
  end
end

Async do 
  host    = "localhost"
  ports   = Range.new(1, 8080)
  timeout = 1.0
  
  limits     = Process.getrlimit(Process::RLIMIT_NOFILE)
  batch_size = [512, (limits.first * 0.9).ceil].min
  semaphore  = Async::Semaphore.new(batch_size)

  ports.each do |port|
    semaphore.async do
      scan_port(host, port, timeout)
    end
  end
end