wait-for.clj

;; Based on a queue polling function from Chas Emerick's bandalore:
;;     https://github.com/cemerick/bandalore/blob/master/src/main/clojure/cemerick/bandalore.clj#L124

(defn wait-for
 "Invoke predicate every interval (default 10) seconds until it returns true,
  or timeout (default 150) seconds have elapsed. E.g.:

      (wait-for #(< (rand) 0.2) :interval 1 :timeout 10)

  Returns nil if the timeout elapses before the predicate becomes true, otherwise
  the value of the predicate on its last evaluation."
 [predicate & {:keys [interval timeout]
               :or {interval 10
                    timeout 150}}]
 (let [poller (fn poller [waiting]
                (if-let [result (predicate)]
                  result
                  (if (<= (+ waiting interval) timeout)
                    (do
                      (Thread/sleep (* interval 1000))
                      (recur (+ waiting interval))))))]
   (poller 0)))