   #
   # **Usage:**
   #
-  #     queue.recently_finished_tasks (tasks) -> YOUR CODE
+  #     queue.recently_finished_tasks (err, tasks) -> YOUR CODE
   recently_finished_tasks: (callback) =>
     @redis.lrange @key('RECENT'), 0, -1, (err, res) ->
       return callback err if err

  #     - poll task from the `SOURCE` queue.
  #   + **failed**, then inspect the passed in argument, retry or block
  #   according to the `do` property of the error object.
  #
  #
  # Calling the callback function is the responsibility of you. Otherwise
  # `Fairy` will stop dispatching tasks.

  #
  # **Usage:**
  #
  #     queue.processing_tasks (err, tasks) -> YOUR CODE
  processing_tasks: (callback) ->
    @redis.hvals @key('PROCESSING'), (err, res) ->
      return callback err if err
