gistfile1.rb

# exponential random backoff ala ethernet
# Nate Murray, 2008
# inspired by code found in http://files.rubyforge.vm.bytemark.co.uk/rhb/xmpphttpbind.rb
class EthernetBackoff
  class Error < StandardError
  end

  # Retries block with exponential random backoff ala ethernet The retry is
  # based on the return value of &block. If the value evaluates to a boolean
  # true then the value is returned. Otherwise it will sleep for the calculated
  # time.
  #
  # The +attempt+ number and +next_backoff_time+ are yielded to the block.
  # +next_backoff_time+  is useful if you want to say how much longer you are going to sleep
  # if the value of your block was false. +attempt+ starts at 0.
  #
  # Example usage:
  #
  #   value = EthernetBackoff.backoff(retries=5) do |attempt, backoff_time|
  #     if attempt + 1 == 3
  #       "happy brick"
  #     else
  #       STDERR.puts("something failed " + "#{attempt+1}/#{retries} (backing off " + "#{sprintf("%.2f", backoff_time)} seconds)")
  #       false
  #     end
  #   end
  # 
  #   value.should eql("happy brick")
  # 
  def self.backoff(retries=10, retry_period=0.5, opts={}, &block)
    retries.times do |attempt|
      next_backoff_time = rand * retry_period * (2 ** attempt)
      value = yield attempt, next_backoff_time

      if value # then we're done
        return value
      else     # we need to try again
        sleep(next_backoff_time)
      end
    end
    # if we're here then we failed
    raise Error, "Retrying failed after #{retries} times. "
  end
end