gistfile1.clj

(ns tt)

(defn deduct-money-from-accnt
  [a1-ref a2-ref {:keys [ensure1 ensure2]}]
  (dosync
    (when ensure1 (ensure a1-ref))
    (when ensure2 (ensure a2-ref))
    (let [sum (- (+ @a1-ref @a2-ref) 200)]
      (when (>= sum 0)
        (alter a1-ref - 200)))))

(defn deduct-money-concurrently
  [a1-ref a2-ref m]
  (let [fut1 (future (deduct-money-from-accnt a1-ref a2-ref m))
        fut2 (future (deduct-money-from-accnt a2-ref a1-ref m))]
    (deref fut1)
    (deref fut2)
    (println (str "Amounts=[" @a1-ref "," @a2-ref "]"))))

(defn transaction-simul
  [{:keys [ensure1 ensure2] :as m}]
  (dorun (repeatedly 10 #(time (deduct-money-concurrently (ref 100) (ref 100) m)))))