queue.rb

require 'thread'

queue = Queue.new
(1..1000).each { |i| queue.push i }

threads = []
concurrency = 5
concurrency.times do |thread_id|
  threads << Thread.new(thread_id) { |id|
    until queue.empty?
      print "Thread (#{id}) pop #{queue.pop}\n"
      sleep rand(10) / 10
    end
  }
end

threads.each { |th| th.join }