Test atomicity

gistfile1.clj

  (defn swap-items-in [atm v1 v2 i1 i2]
    (swap! atm
      (fn [integer-vecs]
        (let [first-vec   (integer-vecs v1)
              second-vec  (integer-vecs v2)
              first-item  (first-vec i1)
              second-item (second-vec i2)
              next-first-vec  (assoc first-vec i1 second-item)
              next-second-vec (assoc second-vec i2 first-item)]
          (assoc
            (assoc integer-vecs v1 next-first-vec)
            v2 next-second-vec)))))

  (testing "swap! is an atomic operation"
    (let [distinct-items 50
          vec-size 10
          integer-vecs (vec (map vec (partition vec-size (range distinct-items))))
          atm (atom integer-vecs)
          thread-count 1
          iterations-per-thread 100]
      (dorun
        (apply pcalls
          (repeat thread-count
            #(dotimes [_ iterations-per-thread]
              (let [v1 (rand-int (/ distinct-items vec-size))
                    v2 (rand-int (/ distinct-items vec-size))
                    i1 (rand-int vec-size)
                    i2 (rand-int vec-size)]
                (swap-items-in atm v1 v2 i1 i2))))))
      (is (= (range distinct-items) (sort (flatten (deref atm)))))))