updated ref example

refs.clj

(import [java.util.concurrent Executors])

(defn test-stm [nitems nthreads niters]
  (let [refs (map ref (replicate nitems 0))
        pool (. Executors (newFixedThreadPool nthreads))
        tasks (map (fn [t]
                     (fn []
                       (dotimes [n niters]
                                (sync nil
                                      (doseq [r refs]
                                              (ref-set r (+  @r t)))))))
                   (map inc (range nthreads)))]
    (. pool (invokeAll tasks))
    (. pool (shutdown))
    (map deref refs)))

(test-stm 10 10 10000)
;; => (550000 550000 550000 550000 550000 550000 550000 550000 550000 550000)