Throttle Hack

book.rb

class Book
  extend Throttle

  def self.sales_rank(isbn_13)
    throttle(1.second) do
      # Do stuff with Amazon Product API that's rate limited to 1 req/s.
    end
  end
end

throttle.rb

module Throttle

  # Terrible, awful, blocking, not thread-safe throttle
  def throttle(duration)
    @_last_throttled ||= duration.ago
    now = Time.now
    elapsed = now - @_last_throttled
    sleep(duration - elapsed) if elapsed < duration
    @_last_throttled = Time.now
    return yield
  end
end