A quick Riemann stream to emit an event when X events are zero

gistfile1.clj

(defn zero-for-count
  "A sliding window of the last n events, emitting an event when all are zero."
  [n & children]
  (let [window (ref (vec (repeat n nil)))]
    (fn [event]
      (dosync (alter window pop)
              (ref-set window (into [(:metric event)] @window)))
      (when (every? (fnil zero? 1) @window)
          (call-rescue
            (assoc event :description (str "Last " n " metrics have been zero!") :state "warning")
              children)))))