transient_thread_test.clj

(defn race
  "Runs two fns in tight loops in two parallel threads for 1 second"
  [publish-fn check-fn]
  (println "---")
  (let [*run?     (volatile! true)
        *failures (volatile! 0)
        thread!   #(future
                     (loop [i 0]
                       (% i)
                       (if @*run? (recur (inc i)) i)))
                     
        *t1   (thread! publish-fn)
        *t2   (thread! #(when-not (check-fn %)
                          (vswap! *failures inc)
                          (println "failure at step" %)))]
    (Thread/sleep 1000)
    (vreset! *run? false)
    { :runs     @*t1
      :checks   @*t2
      :failures @*failures }))
   


(defn race-set
  "Checks set implementation: are insertions made by one thread visible from another?"
  [ctor conj contains?]
  (let [*value (volatile! (rand))
        *set   (volatile! (ctor [@*value]))
        
        publish  (fn [_] ;; publish gurantees that value is ALWAYS in a set
                   (let [next-value (rand)]
                     ;; it first puts value into a set
                     (vswap! *set conj next-value)
                     ;; only then it updates value ref
                     ;; fact: when we observe value it means it was already put in a set
                     (vreset! *value next-value)))
                 
        check    (fn [_] ;; checks if value is visible in a set
                   (let [value @*value
                         set   @*set]
                     ;; fact: if we observe some value it was already put in a set
                     (contains? set value)))]
    
    (race publish check)))
  

;; transient sets fails race-set
;; presumably because it uses mutable Object[] in ArrayNode/BitmapIndexedNode
;; (your results may vary. Better to run `race-set` multiple times)
;; ---
;; failure at step 3287
;; failure at step 229042
;; failure at step 2717018

(race-set #(transient (set %))
          conj!
          #(.contains ^clojure.lang.ITransientSet %1 %2))


;; persistent set is ok
(race-set set conj contains?)