produtorConsumidor.rb

require 'colorize'
require 'thread'

$semaphore = Mutex.new
$phore = Mutex.new
$buffer = []

$cv = ConditionVariable.new

class Consumidor
  def run
    while true do
      $semaphore.synchronize {
        if $buffer.length > 0 then
          $buffer.pop
        else
          $cv.signal
          $cv.wait($semaphore)
        end

        print "#{$buffer.length}".blue
      }
    end
  end
end

class Produtor
  def run
    while true do
      $semaphore.synchronize {
        if $buffer.length < 19 then
          $buffer << rand(100)
        else
          $cv.signal
          $cv.wait($semaphore)
        end
        print "#{$buffer.length}"
      }
    end
  end
end

threads = []
threads << Thread.new { new Consumidor.new.run }
threads << Thread.new { new Produtor.new.run }
# executando threads
threads.each(&:join)