blocking_queue.rb

require 'thread'

MAX_THREADS = 5

class BlockingQueue
  def initialize
    @mutex = Mutex.new
    @got_one = ConditionVariable.new
    @store   = []
  end

  def push(val)
    @mutex.synchronize do
      @store.push(val)
      @got_one.signal
    end
  end

  def pop
    @mutex.synchronize do
      @got_one.wait(@mutex) if @store.empty?
      @store.pop
    end
  end
end

@queue = BlockingQueue.new

MAX_THREADS.times.map do |name|
  Thread.new do
    sleep(rand(10))
    @queue.push(Time.now.to_s + ' ' + name.to_s)
  end
end

collected = 0

until collected >= MAX_THREADS do
  puts @queue.pop.inspect
  collected += 1
end