Boot tasks: run tasks in the background, etc.

build.clj

(def bgs
  "List of tasks running in other threads that will need to be cleaned up before
  boot can exit."
  (atom ()))

;; cleanup background tasks on shutdown
(-> (Runtime/getRuntime)
  (.addShutdownHook (Thread. #(doseq [job @bgs] (future-cancel job)))))

(deftask once
  "Evaluate the `task` only once. Subsequent evaluations will pass through."
  [task]
  (let [ran? (atom false)
        run? (partial compare-and-set! ran? @ran?)]
    (fn [continue]
      (let [task (task continue)]
        #(continue ((if (run? true) task identity) %))))))

(deftask wait
  "Wait for msec milliseconds before calling its continuation."
  [msec]
  (with-pre-wrap (Thread/sleep msec)))

(deftask bg
  "Run the given `task` once, in a separate thread."
  [task]
  (once
    (with-pre-wrap
      (swap! bgs conj (future ((task identity) *event*))))))