periodic_reactor.rb

require 'time'

class PeriodicExecutor

  attr_reader :next_time_to_run

  def initialize(secs, &block)
    @secs = secs
    @block = block
    @next_time_to_run = Time.now.to_f
  end

  def call()
    @next_time_to_run = Time.now.to_f + @secs
    @block.call()
  end

  def <=>(other)
    @next_time_to_run <=> other.next_time_to_run
  end
end

class PeriodicReactor

  def initialize()
    @executors = []
  end

  def add_periodic_executor(secs, &block)
    @executors << PeriodicExecutor.new(secs, &block)
    @executors.sort!
  end

  def run()
    while true and @executors.size != 0
      while Time.now.to_f >= @executors.first.next_time_to_run
        @executors.first.call()
        @executors.sort!
      end
      sleep(@executors.first.next_time_to_run - Time.now.to_f)
    end
  end
end

if __FILE__ == $0
  r = PeriodicReactor.new
  r.add_periodic_executor(3) do
    puts "A"
  end
  r.add_periodic_executor(5) do
    puts "B"
  end
  r.run()
end