Simple Ruby threadpool

threadpool.rb

require 'set'
require 'thread'

module Prod

  # A simple thread pool for running N parallel jobs.
  #
  #  pool = ThreadPool.new(5)
  #  20.times do
  #    pool.next_thread{ sleep 2 }
  #  end
  #  pool.join
  #
  class ThreadPool
    def initialize(num_threads)
      @n = num_threads
      @pool = Set.new
      @mutex = Mutex.new
      @cv = ConditionVariable.new
    end
    def next_thread
      wait_for_opening do
        @pool.add(Thread.new do
          yield
          remove_thread Thread.current
        end)
      end
    end
    def join
      @mutex.synchronize { @cv.wait(@mutex) while !@pool.empty? }
    end
  protected
    def wait_for_opening
      @mutex.synchronize do
        @cv.wait(@mutex) while @pool.size == @n
        yield
      end
    end
    def remove_thread(thread)
      @mutex.synchronize do
        @pool.delete thread
        @cv.signal
      end
    end
  end

end # module