reactor.rb

require 'async'

reactor = Async::Reactor.new

reactor.async do |task|
  task.async do |subtask|
    loop do
      puts 'ping'
      subtask.sleep 3
    end
  end

  task.async do |subtask|
    loop do
      puts 'pong'
      subtask.sleep 4
    end
  end
end

reactor.run