futures with main thread block

stuff.clj

(do
  (def doit (promise))

  (def status (atom 0))

  (defmacro dowork [& forms]
    `(do
       (swap! status inc)
       ~@forms
       (swap! status dec)))

  (def work [(fn [] (dowork (prn "i'm working...") (Thread/sleep 1000)))
             (fn [] (dowork (prn "i'm working...") (Thread/sleep 1000)))])

  (add-watch status :done? (fn [_ _ o n] (when (= n 0) (deliver doit true))))

  (doseq [w work]
    (future (w)))

  (prn "waiting...")
  @doit
  (prn "done"))