Short-circuiting logical conjunction of several futures' values

thread_and.clj

(defn thread-and
  "Computes logical conjunction of return values of fs, each of which
  is called in a future. Short-circuits (cancelling the remaining
  futures) on first falsey value."
  [& fs]
  (let [done (promise)
        ret  (atom true)
        fps  (promise)]
    (deliver fps (doall (for [f fs]
                          (let [p (promise)]
                            [(future
                               (if-not (swap! ret #(and %1 %2) (f))
                                 (deliver done true))
                               (locking fps
                                 (deliver p true)
                                 (when (every? realized? (map peek @fps))
                                   (deliver done true))))
                             p]))))
    @done
    (doseq [[fut] @fps]
      (future-cancel fut))
    @ret))

(comment

  (thread-and (constantly true) (constantly true))
  ;;= true

  (thread-and (constantly true) (constantly false))
  ;;= false

  (every? false?
          (repeatedly 100000
                      #(thread-and (constantly true) (constantly false))))
  ;;= true

  ;; prints :foo, but not :bar
  (thread-and #(do (Thread/sleep 1000) (println :foo))
              #(do (Thread/sleep 3000) (println :bar)))

  )