def client
  Mysql2::EM::Client.new(
    :host => "localhost",
    :username => DbConfig['user'],
    :password => DbConfig['password'],
    :database => DbConfig['database'])
end

def query(query, &block)
  new_client = client
  result = new_client.query(query)
  result.callback do |results|
    block.call(results)
    new_client.close
  end
end

EM::run do
  query("SELECT * FROM USERS") do |users|
     # ...
  end
end