exponential_backoff.rb

# Exponential backoff using Ruby lambdas
#
# Continuously retry sending a request at exponentially increasing
# values, with a top at 1 second

num_retries = 5

exp_backoff = ->(i) { [1, (0.5 * (2.0**(i/2.0) - 1.0))].min }

# stores the delays
(delays ||= [ ]) << (1..num_retries).map(&exp_backoff)

begin
  req = Net::HTTP.get('http://google.com')
rescue StandardError, TimeoutError => e
  if delay = delays.shift
    sleep delay
    retry
  else
    raise StandardError, "Unable to retrieve website: #{e.message}"
  end
end

puts retries
# [0.2, 0.5, 0.9, 1, 1]