thread3.rb

@queue = Queue.new
@queue.push(url: '/foo')
workers = (0...CONCURRENCY).map do
  Thread.new do
    while options = @queue.pop
      begin
        make_request(options)
      rescue => e
        retry_request(options)
      end
      @queue.close if @queue.num_waiting == CONCURRENCY - 1
    end
  end
end
workers.each(&:join)