Simple Ruby thread pool as per http://burgestrand.se/code/ruby-thread-pool/

pool.rb

require 'thread'

module Alert
  def self.yikes(msg)
    # Use this to log/trigger monitor
    puts msg
  end
end

# See http://burgestrand.se/code/ruby-thread-pool/

class Pool
  LOW_ALERT_LIMIT = 10
  HIGH_ALERT_LIMIT = 20

  def initialize(size)
    @size = size
    @jobs = Queue.new
    @pool = Array.new(@size) do |inx|
      Thread.new do
        Thread.current[:id] = inx
        catch(:exit) do
          loop do
            job, args = @jobs.pop
            job.call(*args)
          end
        end
      end
    end
  end

  def schedule(*args, &block)
    @jobs << [block, args]
    if @jobs.length > HIGH_ALERT_LIMIT
      Alert.yikes("Over HIGH alert limit on queue in thread! #{Thread.current[:id]}")
    elsif @jobs.length > LOW_ALERT_LIMIT
      Alert.yikes("Over low alert limit on queue in thread #{Thread.current[:id]}")
    end
  end

  def shutdown
    @size.times do
      schedule { throw :exit }
    end
    @pool.map(&:join)
  end
end