Macruby and Rubymotion GCD groups explanation

movie_night.rb

group = Dispatch::Group.new
derpina_queue = Dispatch::Queue.concurrent(:high)   #Dispatch::Queue.concurrent("com.company.movie_night.get_wine")

derp_queue = Dispatch::Queue.concurrent(:default)   #Dispatch::Queue.concurrent("com.company.movie_night.get_popcorn")

derpina_queue.async(group) do
  puts "go to wine cellar to get some Bordeaux" 
  i = 0
  while i < 99
    puts "can't decide which one to drink"
    i += 1
  end
end
group.notify(derpina_queue) { warn "Derpina is back :-)" }

derp_queue.async(group) do
  puts "go to the kitchen pick some popcorn"
  i = 0
  while i < 9999
    puts "damn, I have to make new one"
    i += 1
  end
end
group.notify(derp_queue) { warn "Derp is back :-)" }

group.wait
puts "both are back, let's watch the movie"

movie.play