producer_consumer.rb

class ProducerConsumer
  KILL = :kill

  def initialize(produce:, consume:, producer_num: 1, consumer_num: 5, max_queue_size: 1000)
    @produce = produce
    @consume = consume
    @consumer_num = consumer_num
    @producer_num = producer_num
    @ids_index = 0
    @max_queue_size = max_queue_size
    @ids_index_mutex = Mutex.new
  end

  def run
    queue = SizedQueue.new(@max_queue_size)

    producers = Array.new(@producer_num) { create_worker(method(:produce), queue) }
    consumers = Array.new(@consumer_num) { create_worker(method(:consume), queue) }

    producers.each(&:join)

    consumers.size.times { queue.push :kill }
    consumers.each(&:join)
  end

  private

  def create_worker(func, *args)
    Thread.new do
      loop { break if KILL == func.call(*args) }
    end
  end

  def produce(queue)
    values = @produce.call(next_ids_index)
    return KILL if kill_worker?(values)
    queue.push(values)
  end

  def consume(queue)
    values = queue.pop
    return KILL if kill_worker?(values)
    @consume.call(values)
  end

  def next_ids_index
    i = nil
    @ids_index_mutex.synchronize do
      i = @ids_index
      @ids_index += 1
    end
    i
  end

  def kill_worker?(v)
    v == KILL
  end
end

nested_ids = [*1..100].each_slice(10).to_a

fetch = proc do |i|
  ids = nested_ids[i]
  next :kill unless ids
  ids.map { |id| id * 2 }
end

insert = proc do |values|
  p values
end

ProducerConsumer.new(produce: fetch, consume: insert, producer_num: 5, consumer_num: 1).run

# $ ruby producer_consumer.rb                                                                                                                                          1:44
# [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
# [22, 24, 26, 28, 30, 32, 34, 36, 38, 40]
# [42, 44, 46, 48, 50, 52, 54, 56, 58, 60]
# [62, 64, 66, 68, 70, 72, 74, 76, 78, 80]
# [82, 84, 86, 88, 90, 92, 94, 96, 98, 100]
# [102, 104, 106, 108, 110, 112, 114, 116, 118, 120]
# [122, 124, 126, 128, 130, 132, 134, 136, 138, 140]
# [142, 144, 146, 148, 150, 152, 154, 156, 158, 160]
# [162, 164, 166, 168, 170, 172, 174, 176, 178, 180]
# [182, 184, 186, 188, 190, 192, 194, 196, 198, 200]