Producer Consumer problem with locks

prod_cons.rb

class Cook
  def produce
    "item"
  end
end

class Consumer
  def consume(item)
    #do something with item
  end
end

class Executor
  MAX_ITEMS = 10
  
  def self.execute
    items = []
    semaphore = Mutex.new
    
    pt = Thread.new do
      producer = Cook.new
      while true do
        semaphore.synchronize {
          if items.size < MAX_ITEMS
            items.push producer.produce 
            puts Thread.current.to_s + " Produced item ... Stock : " + items.size.to_s
          end
        }
        sleep 2
      end
    end

    ct = Thread.new do
      consumer = Consumer.new
      while true do
        semaphore.synchronize {
          if items.size > 0
            consumer.consume items.pop 
            puts Thread.current.to_s + " Consumed item ... Stock : " + items.size.to_s
          end
        }
        sleep 2
      end
    end
    
    pt.join
    ct.join
  end
end

Executor.execute