gistfile1.txt

(def *recently-popped* (ref nil))
(defn pop-log
  "Pop the oldest entry from the log; return nil if none available"
  []
  (when-not (empty? @incoming-log)
    ;; wait till last update of incoming-log is done
    (while (and (not (nil? @*recently-popped*))
                (= @*recently-popped* (peek @incoming-log)))
      (Thread/sleep 100))
    (let [peeked (peek @incoming-log)]
      (send incoming-log pop)
      (dosync (alter *recently-popped* (fn [_] peeked)))
      peeked)))