te_nsqjs/src/backofftimer.coffee

NodeJS client for NSQ

decimal = require 'bignumber.js'

min = (a, b) ->
  if a.lte b then a else b

max = (a, b) ->
  if a.gte b then a else b

###
This is a timer that is smart about backing off exponentially when there
are problems

Ported from pynsq:
  https://github.com/bitly/pynsq/blob/master/nsq/BackoffTimer.py
###
class BackoffTimer

  constructor: (minInterval, maxInterval, ratio = .25, shortLength = 10,
    longLength = 250) ->

    @minInterval = decimal minInterval
    @maxInterval = decimal maxInterval

    ratio = decimal ratio
    intervalDelta = decimal @maxInterval - @minInterval
    # (maxInterval - minInterval) * ratio
    @maxShortTimer = intervalDelta.times ratio
    # (maxInterval - minInterval) * (1 - ratio)
    @maxLongTimer = intervalDelta.times decimal(1).minus ratio

    @shortUnit = @maxShortTimer.dividedBy shortLength
    @longUnit = @maxLongTimer.dividedBy longLength

    @shortInterval = decimal 0
    @longInterval = decimal 0

  success: ->
    @shortInterval = @shortInterval.minus @shortUnit
    @longInterval = @longInterval.minus @longUnit
    @shortInterval = max @shortInterval, decimal 0
    @longInterval = max @longInterval, decimal 0

  failure: ->
    @shortInterval = @shortInterval.plus @shortUnit
    @longInterval = @longInterval.plus @longUnit
    @shortInterval = min @shortInterval, @maxShortTimer
    @longInterval = min @longInterval, @maxLongTimer

  getInterval: ->
    @minInterval.plus @shortInterval.plus @longInterval

module.exports = BackoffTimer